为什么不可说They had finished that work yesterday而要说They finished that work yesterday?

......of what they had seen为什么要加of? _______ experience they had! 英译汉-They had They/re talking as if they had been old friends?从句为什么是”had been "不是”were" They had done that before 为什么第一义不可说 After they had a rest, they went on ___ They had learned 3000 English words ____. They had a good preparation for the project,so they had little__all the work. they've got a toothache还是they have a ...还是they've had a ...?