# 现在完成时
表示动作发生在过去，已经完成，但是对现在造成了影响或后果，动作可能还会持续。
可使用的时间状语为：`already已经 yet还`
形式为：have + 动词过去分词
```
They have already arrived in Shanghai.
She has played soccer for 3 hours.
She hasn't finished the homework yet.
```
# 过去完成时
表示句中的动作发生在过去之前，即过去的过去，已经完成，对过去造成了一定的影响或后果。
形式为：had(have的过去式) + 动词过去分词
```
They had arrived in Shanghai.
She had played soccer for 3 hours.
They hadn't finished the work yet.
```
