（） 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
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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
All of the following are mentioned in the passage as contributing to the ability to play modem violin music EXCEPT（）
A. more complicated techniques for the left hand
B. different ways to use the fingers to play very high notes
C. use of rare wood for the fingerboard and neck
D. minor alterations to the structure of the instrument
与红细胞成熟有关的维生素是
A. 维生素B1和遍多酸
B. 维生素B12和叶酸
C. 维生素B6和叶酸
D. 遍多酸和叶酸
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