可复性关节盘前移位时弹响杂音的特点是()
A.开口初期或开口初、闭口末清脆单声弹响
B.开口末、闭口初清脆单声弹响
C.多声破碎声
D.连续摩擦声
E.一般无弹响
参考答案:A
The agency, ______ to set and enforce health standard for American workers, has been promising a cotton dust standard for several years.
A.which is
B.which it is
C.whose job it is
D.of whose job is
正弦交流电的周期与角频率的关系互为倒数的。