问题
选择题
He doesn't think the question of ________ they are boys or girls is important.[ ]
A. if
B. whether
C. which
D. that
答案
答案：B
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He doesn't think the question of ________ they are boys or girls is important.[ ]
A. if
B. whether
C. which
D. that
答案：B
时，两细线内的张力均为零
时，两细线内的张力均为零