例子A:
The sample started to react with carbon when it was roasted in the air at 900°C.
能否改成“The sample started to react with carbon when (it was) roasted in the air at 900°C.” 也就是省略it was.
另外还有一个例子
例子B
After the sample was roasted in the air for 1 h, the sample started to react with carbon.
能否改成“After being roasted in the air for 1h, the sample started to react with carbon”