GIẢI THÍCH VÌ SAO CHỌN ĐÁP ÁN ĐÓ NHÉ Big cities have problems with, crowded streets, congested traffic, noise and air pollution. Every day, thousands of vehicles ....(47)...... the streets, especially. during rush hours. The large numbers of cars, buses .....(48).... trucks cause so much congestion. No vehicles can move in any direction. Parking' is .......(49)...... problem. There are not enough parking facilities, and when cars try to park ........(50).... the streets, there is not enough room for traffic. Finally, the traffic adds to the problem of air and noise pollution. 47. A.fills B. filled C.fill D.filling 48. A.or B.but C.and D.so 49. A.an B.others C.other D.another 50. A.to B.at C.on D.of