知识梳理：
1.L7. Once out in the street, she walked towards …. bus.
1. 一旦出版，这本词典会非常畅销。Once__________, this dictionary will be very popular.
2. 一旦被抓，他会受到惩罚。Once _________, he will be punished.
3.When ________, it is of great help to learn some skills.
A. reading B. read C. to read D. students read
4. When ________ (tell) the truth, he lost his mind.
