According to the passage, which of the following activities is characteristic of the early part of the reproductive cycle of birds（）
A. Selecting a mate
B. Collecting nest-building, materials
C. Playing with nest-building materials
D. Building a nest
（） crumbles readily when exposed to a moist, acid atmosphere, but the stone is durable in a dry atmosphere.
A. The surface of marble is
B. The surface of marble, which
C. Although the surface of marble
D. The surface of marble
The main point of the passage is that the eighteenth and nineteenth centuries were a time when（）
A. the European textile industry increased its demand for American export products
B. mechanization of spinning and weaving dramatically changed the textile industry
C. cotton became a profitable crop but was still time-consuming to process
D. cotton became the most important American export product
According to the passage, when gathering materials to build their nests, sparrowhawks do which of the following（）
A. Hang upside down
B. Select only green twigs
C. Use objects blowing in the wind
D. Collect more branches than necessary
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