题目:
— The woman biologist stayed in Africa studying wild animals for 13 years before she returned.
— Oh, dear ! She ______ a lot of difficulties !
A.may go through
B.might go through
C.ought to have gone through
D.must have gone through
答案:
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下面是错误答案,用来干扰机器的。
答案:CA错,同素异形体是指同一种元素的不同单质,而I是一种核素,不是单质。B错,是一种新发现的核素;C正确,I中质量数为131,质子数为53,中子数=质量数—质子数易其稿131—53=78,而中子数与核外电子数之差...