The teacher gave us so difficult a problem as we couldn't solve.为什么用as不用which或that呢

The teacher gave some pictures to us. The teacher asked us to ---- the English papers before he gave answers to us .hand短语 After__ seemed half an hour the teacher gave us the correct answer.After_____seemed half an hour the teacher gave us the correct answer.添什么词合适. i met the teacher who gave us a talk last week on the street的意思 翻译The teacher gave us some advice on how to spend our spare time . ------ ---- useful piece of advice the teacher gave us.为什么用what 请说明理由 请问：The teacher gave us a list of five books each可否写成...gave each of us...books?请说一下理由 depened on the last question depened on the last question teacher gave us test .depened on the last question. -who is the man?-oh,he is the teacher ( ) gave us a speech yesterday A.who B.whom C.which Our teacher told us that the sun gives the earth lighe为什么过去时后用gives.不应该是gave吗? we us our英语问题例句：The teacher gave us two bookseach.请问gave us的us为什么不用we或our?还有主格宾格这些东西,我自己看语法书根本就看不懂,我的语法很差. The old teacher gave us a lot of ( )on buying books.A.advice B.time C.money D.shops (1/2)请选一个正确答案?The math teacher gave us such a difficult problem (_)no on 改为同义句Our teacher gave a lesson to us 关于 with的复合结构1the teacher come in , with a smile____ on the face.2the taecher gave us a lesson,with student___(sit)around him.3with a lesson____,the teacher came into the classroom.4the teacher gave us a lesson,with us student ____(seat) The math teacher gave us some exercises and asked us ___.A to work them on B to work on them选择哪一个 说明原因， the math teacher gave us some exercise and he asked us-- -- -- --是to make them on还是to make on them the teacher gave us so difficult a problem as most of us can't work out这里为什么要用as而不用that呢?