No one could play by ear.

我能够凭听觉而不是识谱来演奏音乐。

I can't play by ear, and I know you used to be able to do that.

我不能用耳朵弹奏，但是我知道你可以这样做。

When he is coming, I don't know what should be say, I will play by ear at that time.

我没有时间准备这个会议，到时讲到哪里算哪里。

I don't know what they'll want when they arrive—we'll have to play it by ear.

我不知道他们到达时需要什么—我们只有见机行事了。

So the WHO has decided to play it by ear, and given the unpredictability of flu, this is probably not a bad thing.

因此，世卫组织已经决定让出发言权。因为流感的标准存在不确定性，所以这样做或许也不是一件坏事。