3. In other words, there are three times as many girls as boys.
也就是說，女生人數是男生的三倍。
表示A是B的幾倍時，常用以下句式：
(1)A is x times as＋形容詞(或副詞)原級＋as B
There is x times as many＋可數名詞復數＋as B
There is x times as much＋不可數名詞＋as B
(2)A is x times＋形容詞(或副詞)比較級＋than B
(3)A is x times＋the size / height / length / width＋of B

4. Oh really? So have I. Which language are you studying?
哦,是嗎？我也是。你在學什么語言？
“so +助動詞/情態動詞/系動詞+主語”表示“(另一事物)也……”
He is sixteen, so am I.
他16了，我也是。
Tom likes playing football, so do I.
湯姆喜歡踢足球,我也是。
(1)表示否定意義時用“neither/nor +助動詞/情態動詞/系動詞+主語”，意為“(另一事物)也不……”。
He doesn't like math, neither do I.
他不喜歡數學,我也不喜歡(數學)。
I don't know about it, nor/neither do I care.
我不知道這件事,也不關心。
(2)“so +主語+助動詞/情態動詞/系動詞”表示對之前或對方所說的情況表示贊同或證實，意為“(同意一個人或事物)確實……”
— Mary is good at music.
——瑪麗音樂很好。
— So she is.
——是的，的確很好。
— They have moved away.
——他們已搬走了。
— So they have.
——是的，他們已搬走了。
注意：助動詞及其時態的選擇要根據前句確定。
He has finished his homework, so has Mary.(so have the other students.)
他已經完成了他的家庭作業,瑪麗也完成了。(其他學生也完成了。)
The teacher will go to America, so will the students.
老師要去美國,學生們也要去。
（3）So it is / was with me. 我也如此。用于前面句子中并列謂語不同或肯、否定形式不同時。

5. The school year is divided into two semesters, the first of which is September through December, and the second January through May.
一學年有兩個學期,第一學期從九月到十二月,第二學期從一月到五月。
本句中含有一個“介詞+關系代詞”構成的非限制性定語從句。“介詞+關系代詞”引導定語從句時，關系代詞只能用which、whom，不能用that，也不能省略。
We live in a house, in front of which is a small river.
我們住在前面有一條小河的房子里。