Keep one's ears open:
打開(kāi)耳朵 ×
留心聽(tīng)（看）；密切注意 √
例句：
Keep your mouth shut and your ears open.
多聽少講 。
Have a word in somebody's ear:
和某人說(shuō)秘密話(huà) √
例句：
When you have time would you come to my office, I'd like to have a word in your ear.
你有空請來(lái)我辦(bàn)公室，我想同你私下談談。
Couldn't believe my ears:
不敢相信自己的耳朵 ×
不敢相信 √
例句：
I couldn't believe my ears. My boss fired me today.
我不敢相信 ，今天老闆(bǎn)把我解雇瞭(le)。
