Most birds find it safe to sleep in the trees, but ____ they have eggs or young chicks, they don’t use a nest.
A．whyB．howC．unlessD．where
C
unless引導(dǎo)讓步狀語從句,意為“如果不”。根據(jù)they have eggs or young chicks和they don’t use a nest可判斷出前句是后句的條件,表示“如果它們不下蛋或沒有小鳥,它們就不用窩”。why用于引導(dǎo)名詞性從句或定語從句,意為“為什么”。how引導(dǎo)名詞性從句,意為“如何”,表示動作的方式。where引導(dǎo)名詞性從句或定語從句,意為“在……地方”。
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