题目内容
.Most birds find it safe to sleep in the trees, but __________ they have eggs or young chicks, they don’t use a nest.
A. why B. how
C. unless D. where
C。
解析:
将四个选项的意思分别套入句中,只有填unless时意思最通顺。为便于理解,句子也可转换成:Most birds find it safe to sleep in the trees, but they don’t use a nest unless they have eggs or young chicks.
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