乘虚的英文：
take advantage of a weak point

参考例句：

He headed the ball into an open goal,ie one temporarily unprotected by the goalkeeper.
他乘虚把球顶入球门.

This was touching Martin on his weak point, and having him at a great advantage
这话正是打在马丁的病根儿上，捣弱乘虚，让他再也无法抵抗。

take是什么意思：
v. 拿，取；带；获得；采取；承担；吃；耗费；乘，搭；以为；理解；走；抓住

a catch; a take; a taking
捕获量

take a nap; take a snooze
小睡一下;睡午觉

take service with
在￥帮佣

advantage是什么意思：
n. 有利条件；有利因素；优势；益处；利益
v. 使处于有利地位；有利于；得益，获利

to the best advantage
效果最佳地|最出色地

Advantage server!
发球者占先！

Press one's advantage
利用有利形势[优势]进逼

weak是什么意思：
adj. 疲软的；虚弱的；软弱的；愚钝的；不牢固的；淡薄的

a weak radio signal; a weak link.
微弱的无线电信号；薄弱的连接。

He has weak eyes.
她的视力不佳。

The spirit is willing But the flesh is weak
力不从心。