单项选择题
A．A historical theory is sketched and a problem with the theory is cited.
B．Evidence for an objection to a theory is mentioned and a generalization from that evidence is advanced.
C．A paradox about the origins of a historical phenomenon is pointed out and the author's explanation of the paradox is expounded.
D．A statement about a historical phenomenon is offered and a possible misinterpretation of that statement is addressed.
E．A new explanation for a historical phenomenon is given and evidence for that explanation is provided.
单项选择题 The passage is primarily concerned with（）
单项选择题 According to the passage, astronomers studying Martian meteors discovered on Earth were perplexed by them for which of the following reasons（）
单项选择题 Which of the following, if true, would cast most doubt on the conclusions drawn from Head's higher-resolution models（）