1.改正：He succeeded in the competition,which made each of us happy.
或：He succeeded in the competition,making each of us happy.
不能用两个动词同时做一个简单句的谓语.
要么把句子变成复合句,要么把某个动词变成非谓语形式.
2.改正：The problem is that more and more young people are getting into the habit of smoking.
表语从句的that不能省略.
3.改正：Whether he is an engineer is unkown.
主语从句的“是否”只能用whether,不能用if.
4.改正：What she wants to know is whether she should attend the conference.
表语从句的“是否”用whether,不能用if.
5.改正：At the meeting he raised a question whether the project would be cancelled.
同位语从句的“是否”用whether,不能用if.
6.改正：It depends on whether it's going to rain.
介词后的宾语从句的“是否”用whether,不能用if.
7.改正：We expressed the hope that the Browns would come to China again.
同位语从句的引导词t不用which用that.
8.改正：The reason why he failed in the exam was that he was too careless.
用表语从句来解释原因时,引导词用that,不用because.
9.改正：Whoever comes to visit the exhibition is welcome.
no matter不能引导主语从句,但是whoever可以.
10.改正：What he needs is enough time and what I need are enough books.
what引导的主语从句,动词的数应该根据事实来判断.