Question

begin 是瞬间动词 为什么还有had begun的用法

Answer 1

had begun : [已经开始了]. 是[过去完成]时态, 并不影响该动词是否瞬间动词. 

[过去完成时]用法: 

表示两组动作发生在过去的不同时间的先后次序. 先完成的动作用[过去完成时],

后完成的动作用[过去时]

例句:

I had eaten an apple when father came home. 

(过去)我吃完了一个苹果后爸爸才回家.

When she arrived,the party had already started.

当她抵达时, 派对已经开始了.

He had been a poor man before he became rich.

在他富有之前他是一个穷人.

The film had already begun by the time we arrived the cinema.

电影在我们抵达戏院时已组放映.

Answer 2

瞬间动词完全可以用于完成时态,表示“……已经开始”.只要不与表示时间段的时间状语连用即可。