that means I can't stand it. 我简直受够了。

I have took part in many speech competitions. First of all, you should prepare well, including the the content of ur speech and some background of ur topic. Good preparations can help u a lot. While, during ur speech, because of lacking experience, u will surely feel nervous.When i first took part in an speech Competition, i was very nervous, since i was afraid of seeing the reactions of the audience. An experienced teacher told me not to look at others directly in their eyes, u just look at a piont above their head. It wil magically work the same! The audience will believe u look at them and make eye contact with them! I tried it and it really works! Hope u will succeed in ur speech contest. Good luck!

the first one is an ellipsis sentence, it is usually used in a formal occasion, while the second one is obviously correct.

两者都可以，第一种的结构I think it important. think 是谓语it 是宾语 important是宾补，补充说明宾语的。 第二种结构 I think it is important 是think 后面加了宾语从句。这个宾语从句省略了引导词 that。