PASSAGE 2 – Questions 11–20

A snowfall consists of myriads of minute ice crystals that fall to the ground in the form of frozen precipitation. The formation of snow begins with these ice crystals in the subfreezing strata of the middle and upper atmosphere when there is an adequate supply of moisture present. At the core of every ice crystal is a minuscule nucleus — a solid particle of matter around which moisture condenses and freezes. Liquid water droplets floating in the supercooled atmosphere and free ice crystals cannot coexist within the same cloud, since the vapor pressure of ice is less than that of water. This enables the ice crystals to rob the liquid droplets of their moisture and grow continuously. The process can be very rapid, quickly creating sizable ice crystals, some of which adhere to each other to create a cluster of ice crystals or a snowflake. Simple flakes possess a variety of beautiful forms, usually hexagonal, though the symmetrical shapes reproduced in most microscope photography of snowflakes are not usually found in actual snowfalls. Typically, snowflakes in actual snowfall consist of broken fragments and clusters of adhering ice crystals.

For a snowfall to continue once it starts, there must be a constant inflow of moisture to supply the nuclei. This moisture is supplied by the passage of an airstream over a water surface and its subsequent lifting to higher regions of the atmosphere. The Pacific Ocean is the source of moisture for most snowfalls west of the Rocky Mountains, while the Gulf of Mexico and the Atlantic Ocean feed water vapor into the air currents over the central and eastern sections of the United States. Other geographical features also can be the source of moisture for some snowstorms. For example, areas adjacent to the Great Lakes experience their own unique lake-effect storms, employing a variation of the process on a local scale. In addition, mountainous sections or rising terrain can initiate snowfalls by the geographical lifting of a moist airstream.

11. Which of the following questions does the author answer in the first paragraph?

PASSAGE 3 – Questions 21–30

Social parasitism involves one species relying on another to raise its young. Among vertebrates, the best-known social parasites are such birds as cuckoos and cowbirds; the female lays an egg in a nest belonging to another species and leaves it for the host to rear.

The dulotic species of ants, however, are the supreme social parasites. Consider, for example, the unusual behavior of ants belonging to the genus Polyergus. All species of this ant have lost the ability to care for themselves. The workers do not forage for food, feed their brood or queen, or even clean their own nest. To compensate for these deficits, Polyergus has become specialized at obtaining workers from the related genus Formica to do these chores.

In a raid, several thousand Polyergus workers will travel up to 500 feet in search of a Formica nest, penetrate it, drive off the queen and her workers, capture the pupal brood, and transport it back to their nest. The captured brood is then reared by the resident Formica workers until the developing pupae emerge to add to the Formica population, which maintains the mixed-species nest. The Formica workers forage for food and give it to colony members of both species. They also remove wastes and excavate new chambers as the population increases.

The true extent of the Polyergus ants’ dependence on the Formica becomes apparent when the worker population grows too large for the existing nest. Formica scouts locate a new nesting site, return to the mixed-species colony, and recruit additional Formica nest mates. During a period that may last seven days, the Formica workers carry to the new nest all the Polyergus eggs, larvae, pupae, every adult, and even the Polyergus queen.

Of the approximately 8,000 species of ants in the world, all five species of Polyergus and some 200 species in other genera have evolved some degree of parasitic relationship with other ants.

21. Which of the following statements best represents the main idea of the passage?

PASSAGE 4 – Questions 31–40

The Winterthur Museum is both a collection and a house. There are many museums devoted to the decorative arts and many house museums, but rarely in the United States is a great collection displayed in a great country house. Passing through successive generations of a single family, Winterthur has been a private estate for more than a century. Even after the extensive renovations made to it between 1929 and 1931, the house remained a family residence. This fact is of importance to the atmosphere and effect of the museum. The impression of a lived-in house is apparent to the visitor; the rooms look as if they were vacated only a short while ago — whether by the original owners of the furniture or the most recent residents of the house can be a matter of personal interpretation.

Winterthur remains, then, a house in which a collection of furniture and architectural elements has been assembled. Like an English country house, it is an organic structure; the house, as well as the collection and the manner of displaying it to the visitor, has changed over the years. The changes have coincided with developing concepts of the American arts, increased knowledge on the part of collectors and students, and a progression toward the achievement of a historical effect in period-room displays. The rooms at Winterthur have followed this current, yet still retained the character of a private house.

The concept of a period room as a display technique has developed gradually over the years in an effort to present works of art in a context that would show them to greater effect and give them more meaning for the viewer. Comparable to the habitat group in a natural history museum, the period room represents the decorative arts in a lively and interesting manner and provides an opportunity to assemble objects related by style, date, or place of manufacture.

31. What does the passage mainly discuss?