问题
选择题
| 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 |
答案
答案：C
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| 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 |
答案：C