He asked what he was doing at that time.

他问他当时在做什么。

At that time, there was much interest in electricity.

当时，人们对电非常感兴趣。

He was not at home at that time.

当时他不在家。

I was reading at that time.

当时我正在读书。

We were all very young at that time.

当时我们都很年轻。

I didn't know what to do at that time.

当时我不知道该怎么办。

Chang'an during the Han dynasty was one of the largest cities in the world at that time.

汉代的长安是当时世界上最大的城市之一。

It was considered a fashion at that time.

这在当时被认为是一种时尚。

It deeply mirrored the social reality at that time.

它深刻地反映了当时的社会现实。

At that time, balalaikas were made by the players themselves.

当时，巴拉莱卡是由球员自己制作的。