a. 副詞子句通常是由一個從屬連接詞 subordinating conjunction 開始一個句子，比方說 although, because, when 等。這個連接詞表達了這個副詞子句跟主要子句之間的關係。
Although the sun’s shining, it’s freezing outside this morning.
I’m not going out because it’s so cold.
Before he goes to bed, he brushes his teeth.
He brushed his teeth before he goes to bed.
Don’t touch the paint before it has dried because bubbles may form if anything touches it.
After you have a rest, you’ll probably feel better.
I can’t listen to music while I’m studying.
2 副詞子句是個非獨立子句，不可以用來當作獨立的句子，一定要與獨立子句合併成為一個句子。副詞子句不可再加上對等連接詞 (如: for, and, nor, but, or, yet, so) 來合併句子。
Because there were no lights, I couldn’t see anything.
It was dark, so I couldn’t do any work.
Because there were no light, so I couldn’t do any work. (X)
We couldn’t use our computers because there was no electricity this morning.
We couldn’t use our computers. Because there was no electricity the morning. (X)
3 某些連接字如 after, before, than 可以當從屬連接詞或介系詞。當從屬連接詞時帶領副詞子句也就是後面加主詞，動詞，來連接句子，也可以當成介系詞用，當介系詞時後面加名詞。
I’ll talk to you after I get out of my next meeting. = I’ll talk to you after the meeting.
Tony had arrived before we got there. = Tony had arrived before us.
We had more money than they had. = We had more money than them.
There were delays because the weather was bad.
= There were delays because of bad weather.
Although she’s old, Agnes still plays tennis.
= Despite her age, Agnes still plays tennis.
He got injured while we were playing.
= He got injured during the game.
A 時間子句 when, while, as, after, before, until, since 等
1.1 when 用來表示一件事接著另外一件事
When we heard the news, we were delighted.
1.2 when 用來在打斷另外一件事時
We had just reached the shelter when the rain started pouring down.
I was sleeping like a baby when the alarm went off.
1.3 when 可以用來表達每一次，有點像 if 的用法，表示每一次發生某事時。
When demand increases, prices rise.
2.1 while 可以表示在某段期間，這時跟 when 可以通用
While/when you were out, your mother called.
I felt asleep while/when I was reading.
2.2 while 也可以用來表示兩件實情同時發生
There was nowhere to park, so I just drove round in the car while Tim was in the bank.
3.1 as 跟 when 跟 while 都可以用來表達再發生某件事的某段期間
As/When/While I was getting ready to leave, I heard that my flight had been canceled.
3.2 as 或是 just as 可以用來強調事件發生的確切時間點，這時不可以用 while
As I walked out of the hotel, a gust of wind blew my hat off. It happened just as I stepped outside.
3.3 as 可以用來表時連接一段期間的變化，這時不可以用 whlile
As I get older, I care less about what other people think.
4.1 after 用來表示在某個時間點之後
After they left, we cleaned up and went to bed.
What will you do after you graduate?
4.2 after 常用在跟現在簡單式與現在完成是而不會用 will 表達一段完成的動作
I’ll help you after I write/have written my report. (not after I will write my report)
5 before 用來表示在某個時間點之前
Before he leaves, I’ll ask him about the money.
They had eaten breakfast before we got up.
6 until 用來表示直到某個時間點，用來強調結局或結束的時間點。
We’ll wait until you’re ready.
Heat the wax until it melts. (not Heat it before it melts)
7 since 用來表達從某個時間點到另外一個時間點，表示在某個時間點開始的另外一個子句的是在那之後能就是事實。
How long is it since you’ve been here?
I’ve lived here since I was ten. (not since I’m ten)
8 once 用來帶領一個子句描述一個動作或情況的開始的時間點。once 跟after 一樣 常用在跟現在簡單式與現在完成來表達一段完成的動作
Once you’ve seen Ani, you won’t forget her.
Everybody likes it here once they get used to it.
9 as soon as 用來表達一件事馬上緊接著另外一件事發生或是 immediately 來帶領子句
I came as soon as I heard the news.
Immediately I saw him, I recognized his face.
10 the instant/minute/moment/second (that) 可以用來表示一件事緊接著另外一件事發生
There are some students who rush out of the room the minute (that) class ends.
1 Because my TV was broken, we listened to the radio.
2 Although it was cold, he still went swimming.
3 He is handsome, but his brother is plain.
4 If it rains tomorrow, the concert will be canceled.
5 As soon as he got home, he turned on his computer.