What does the passage mainly discuss（）
A. How sediments were built up in oceans during the Cretaceous period
B. How petroleum was formed in the Mesozoic era
C. The impact of changes in oceanic animal and plant life in the Mesozoic era
D. The differences between plankton found in the present era and Cretaceous plankton
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SWOT分析的机会与威胁分析将注意力放在（）。
A. 现有竞争对手之间的抗衡
B. 对行业发展现状和前景的综合分析
C. 外部环境的变化及对企业的可能影响上
D. 企业自身的实力及其与竞争对手比较
Hydrofoils can exceed 75 miles per hour, as compared with conventional watercraft, whose maximum speeds （） approach 50 miles per hour.
A. are rarely
B. rarely
C. of rarely
D. they rarely
Which of the following birds are mentioned as those that build nests that include unusual objects（）
A. Ravens
B. Ospreys
Crows
D. Sparrowhawks
The word "it" in line 21 refers to（）
A. biological productivity
B. oil
C. organic material
D. petroleum
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