Exercise 1:
1, Strike while the iron is hot.
2, The chairman introduced the speaker;then he left the hall.
3, We don't necessarily grow wiser as we grow older.
4, The lecturer will come, or he will send a substitute.
5，I can not afford a new car; besides, I have a old Ford.
6, I will not accept the position, nor I want you to take it.
7, You will not be able to keep your appointment unless you hurry.
8, Put the manuscript where the editor can find it.
9, I do the work; he gets the credit!
10, We were so late that we missed the concert.
11, You have broken the law; therefore, you must be punished.
12, Although he is rich, he is not happy.
13, It wil not be long before I came back.
14, You must not waste time in that life is short.
15, Since you insist, I reconsider the matter.
Explaination:
3，随着年龄的增长，我们不一定会变得更聪明。（from google）
Exercise 2:
16, As far as I know, he is very honest.
17, Since she went to New York, her father has not heard from her.
18, She is going to buy a hat after her cash a check.
19, Go and get me some ice cream. (= Go to get me some ice cream.)
20, It is such a snowy day that travel advisories have been issued for most of the major highways.
21, The concert wiil not commence until the conductor arrives.
22, Either you or he is wrong.
23, The sentence "In spite of his wealth, he is not happy." is equal to "Rich as he is, he is not happy."
Although he is rich/wealthy, he is not happy.
24, Smith wrote his first poem while he worked as a porter in a saloon in New York.
25, It is not safe to get out a car until it has come to a stop.
Explaination:
18, 表时间或条件的状语从句中，必须用一般现在时代替一般将来时。
20，这是一个下雪天，大部分主要高速公路已经发行了旅游咨询。（from google）
24, (=...while working as a porter)
Exercise 3:
26, Few of gold seekers who flocked to California were experienced miners,
nor did they feel that they had to be.
27, Even though Juan is studying physics now, he is planning to speed next year studying biology and paleontology.
28, John, a versatile young man, is skilled in both drawing and singing.
29, Nothing is so hard that it will not become easy by practice.
30, I went to see the zoo when I stayed in Bangkok.
Explaination:
26，涌入California的淘金者，没人（没几个人）是有经验的矿工，他们也不认为自己（之前）必须是矿工（才能来淘金）。
29，没什么有（它）这么难，哪怕是通过（多）练习（它）也不会变简单。