Xi'an is a beautiful city, isn't it?

They watched the train until it disappeared in the distance.

2. 也可以指动物或婴儿(未知性别的婴儿或孩子):

Is this your dog？No, it isn't.

二、it作非人称代词

it有时并不指具体的东西，而泛指天气、时间、日期、距离、价值、度量、温度、环境等，称为非人称的it：

1. 指天气：

It is a lovely day, isn't it?

It is a bit windy.

2. 指时间:

It was nearly midnight when she came back.

3. 指环境:

It was very quiet in the café.

4. 指距离：

It is half an hour's walk to the city centre from my home.

5. 指日期：

What's the date today? It's May 1, 2007.

6. 指季节：

It is summer now.

7. 指度量：

It is about 5 kilograms.