影院、礼堂发生火灾后，吊灯掉落时间一般在起火后＿min。
A.15～20
B.20～25
C.25～30
D.30～35
参考答案：A
Was it because it rained heavily last night ______ he didn't come? [ ]
A. why
B. when
C. that
D. then
发电机、变压器发出的声音为
A．机械性噪声B．流体动力性噪声C．电磁性噪声D．脉冲噪声E．稳态噪声
