as mute as a fish 噤若寒蝉；默不作声；守口如瓶

【例句】
Jim did not agree with the teacher,but held his peace as the teacher was rather angry.
吉姆不赞成老师的意见，但是由于老师非常生气，他只好默不作声。

He remained as mute as a fish.
他仍然是默不作声。