下面关于胎心率变异减速的描述哪项不恰当（）

A.减速与宫缩无关系

B.下降迅速且幅度大

C.持续时间长短不一

D.恢复缓慢

E.是脐带受压兴奋迷走神经所致

Tom is _______ learning English. To learn it well, he abandons all his hobbies.

A．bound to

B．desperate to

C．bent on

D．accustomed to