我们开始做某事时，天已经黑了。

It was already dark when we start to do something.

现在才四点，天已经黑了。

It's only four o'clock and it's already getting dark.

我们到达车站时天已经黑了。

It was dark by the time we arrived at the station.

下班的时候，天已经黑了。

When I left the office, the day was dark already.

天已经黑了，我们就在美国的一套旅馆住了下来。

It has been already black , we have lived right away in American set of hotel.

到了九点天已经黑了，由于没有电灯，除了睡觉没有别的事情可做。

By nine it is dark and, as there is no electric lighting, there is little to do but sleep.

当他们从最后一家商店走出来时天已经黑了，乔很疲倦，他正思考着其他的问题。

It was dark when they came out of the last shop, and Joe was tired and thinking about other thing.

“小爱，小爱，外面天已经黑了，你要去哪?你回来……”奶奶倚靠在陈旧的门槛上惶恐地在背后叫喊着。

Xiaoai, Xiaoai, the sky had already been dark. where are you going ? you come back……Granny leaned on the antiquated doorsill and shouted in panic behind her.