天黑了，你最好回家吧。

It's dark now. You'd better go home .

天黑了，请点蜡烛。

It's dark. Please light the candle.

我们犯困是由于我们的身体信号告诉我们的大脑我们累了，环境就是告诉我们天黑了的信号。

We grow sleepy due to signals from our body telling our brain we are tired, and signals from the environment telling us it's dark outside.

如果天黑了，你用手电筒。

If it is dark, you use the flashlight.

外面已经天黑了。

It is already dark outside.

天黑了，我们需要开灯。

It's getting dark; we need to light up.

十分钟内就要天黑了。

It will be dark in ten minutes.

此刻，天黑了，我很累，

It was dark now and I was tired.

你真不方便，天黑了就要回家。

You are really no-go , dark is about to come home.

天黑了，故很难拍到好的相片了。

The day was dark, so to make a good photograph hard to get.