某种苍蝇在飞行时4s内翅膀振动1400次,则频率是 ,而蝴蝶的振动频率是8Hz,即它每秒振动 次,人类能听到的是 发出的声音。
350Hz,8,苍蝇
It ____ that all the students were having lessons in the teaching buildings when the earthquake occurred.[ ]
A. happens
B. was happened
C. happened
D. was happening
养成亲社会行为既有利于社会的和谐,也有利于我们更好地融人社会。下列行为不属于亲社会行为的是( )
A.学校给(1)班5个三好学生名额,班里推荐时,同学们都相互谦让
B.李洋同学把刚买来的数学辅导书给同学们传阅
C.同学们知道刘梅同学因家境贫穷而面临辍学时,都踊跃捐款帮助
D.张颖见别人学唱歌,她也学唱歌;过几天,见别人学跳舞,她也学跳舞