3. I think this is because he really enjoys teaching Chinese literature — he loves it, in fact!
我想這是因為他確實喜歡教中國文學——事實上,他熱愛中國文學！
句中because為連詞,連接一個表原因的表語從句,意為“這是因為……”；而當reason作主語時,其表語從句一般只用that引導,不用because。
①“It / This / That+系動詞+because從句”意為“這/那是因為……”
He is not here. It is because he is ill.
他沒有來是因為他病了。
②“It /This / That+系動詞+ why從句”意為“這/那就是……的原因”。
He is ill. This is why he is not here.
他病了，這就是他沒有來這的原因。
③“The reason +系動詞+that從句”意為“理由是……”
He is not here. The reason is that he is ill.
他沒有來，理由是他病了。

4. He's about 28,I think, and is rather good–looking.
我想他大約28歲，長得相當英俊。
I think為插入語。插入語可以插到一個語法結構已完整的句子里去,做一些附加的說明。后接從句要表達否定時,其否定形式應該前移到主句。作插入語可以是不定式短語、現在分詞短語、介詞短語、形容詞、副詞、從句等。
常見的插入語有：
I think 我認為
I believe 我相信
I guess 我認為
I suppose 我猜想
I,m afraid 我恐怕
as far as I know / remember 據我所知
you see 你曉得
do you know 你知道嗎
do you think 你認為
what's more 此外
that's to say 也就是說
believe it or not 信不信由你
what's worse 使事情更糟糕的是
generally speaking 一般來說
frankly speaking 坦白地說
to tell you the truth 說真的;老實說
to be honest 說實在的
to make matters worse 更糟糕的是
I don't think you are right.
我認為你不對。
I don't suppose I shall be back until 8 o'clock.
我想8點以前我回不來。
I must say, I love that picture of the six horses.
我必須說,我愛有六匹馬的那幅畫。
By the way, where is Xiao Li?
順便問一句，小李在哪兒？(介詞短語)
Worse still, it began to rain heavily.
更糟糕的是,開始下大雨了。(副詞)
I'd really rather not go, if you don't mind.
我確實不想去,如果你不介意的話。(從句)
復雜疑問句/雙重疑問句的組成：
疑問詞+插入語(do you think / believe / guess)+主語+其他
Who do you think will win the game?
你認為誰會贏得這場比賽？
該句式需要注意：
①插入語為一般疑問句形式;
②插入語后面不再加引導詞;
③插入語后接陳述語序。
你認為他在等誰？
Who do you think that he is waiting for? (×)
Who do you think is he waiting for? (×)
Who do you think he is waiting for? (√)