填空. When you are in England, you must be careful in the streets because traffic drives on the left. __ 1 __ you cross a street, you must look to the right first and then left. If the traffic lights are __ 2 __, the traffic must stop. Then the people on the foot can cross the road __ 3 __.If the traffic lights are green, the traffic can go on, people on foot __ 4 __cross. In the morning and in the evening, when people go to or from work, the streets are very __ 5 __.Traffice is most dangerous then. When you go by bus in England, you have to be carefully, too. Always remember that traffic moves on the __ 6 __. So you must be careful. Have a look first, __ 7 __ you will go the wrong __ 8 __. In many English cities, there are big buses __ 9 __ floors. You can sit on the __ 10 __ floor. From there you can see the city very well. It's very interesting. (       )1. A. Before (       )2. A. black (       )3. A. care (       )4. A. can (       )5. A. busy (       )6. A. left (       )7. A. because (       )8. A. street (       )9. A. in (       )10. A. first B. After B. red B. careful B. could B. big B. right B. or B. park B. or B. second C. Between C. g reen C. carefully C. must not C. safe C. front C. so than C. road C. with C. third D. Unit l D. yellow D. more careful D. have to D. wide D. back D. either D. way D. on D. fourth