如果他们今天一早就离开家的话，再过半小时他们就该到了。(从句说明过去，主句说明将来。)

If they had left home early this morning, they would arrive in half an hour.

youdao

如果他们今天一早就离开家的话，再过半小时他们就该到了。(从句说明过去，主句说明将来。)

If they had left home early this morning, they would arrive in half an hour.

youdao