语法问题

40. While studying the chemistry of human body, Dr. Rosalyn Yalow won a Nobel Prize for the research she conducted on the role of hormones.
答案选B,是什么原因呢?(9508,40)

15. Nebraska has floods in some years, _____.
(A) in others drought
(B) droughts are others
(C) while other droughts
(D)  others in drought

答案选A，但为啥不要连词呢？(9508,15)

40。考点：单数可数名词不能单独出现。

15。并列结构。

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