If I were you, I’d take an umbrella.
If you had worked hard, you wouldn’t have failed the exam. 如果你早用功，你就不至于考试不及格了。（与过去事实相反，事实：没用功）
If it were to rain tomorrow, our picnic would be put off.
1. If I _____ you, I’d take the small apple.
A. am B. were C. was
2. What would you do if you ____ a lot of money?
A. had B. have had C. will have
3. We would be very pleased if you _____ (come).
4. What a pity! I haven’t got my car. If I had, I _____ (take) you to the airport.
5. If the old man _____ (be) younger, he would climb over that wall quickly.
6. Where _____ they ______(go) if it rained right now?
7. If Bill _____ (be) here, he would have helped you. 答案：
4. would take
6. would; go
7. had been
1. What would I have done without you?
（本句通过介词短语给出虚拟条件，without you相当于if I had not been with you或if you had not helped me）
2. We didn’t know his telephone number, otherwise we would have telephoned him.
这是陈述句+or else/otherwise +虚拟句句型
A number of the other plants were found in America.
The number of people who travel by plane in China is larger than ever before.
a number of意为“很多”，修饰可数名词复数时谓语用复数 the number of意为“….的数目”，做主语时，谓语用单数 练习：
A number of students in this class _____ here now. (is /are)
A small number of students ___ passed the exam. (have/has) The number of the students in this class ____ fifty. (is/are)