Read the passage and choose the best answer to complete each blank

Traffic jams in Viet Nam frequently (30) _________ place in big cities, such as Ha Noi and Ho Chi Minh City.

There is no fixed rule for the time a traffic jam to happen. But it is worst (31) _________ the rush hour when everyone is in a hurry to get to work or come back home. Apart from peak hours, the time between 9 a.m. to 10 a.m. and between 3 p.m. to 4 p.m. also witnesses long lines of vehicles, mainly motorbikes. (32) _________ it rains, the traffic jam gets more terrible. Taxis are extremely hard to catch or wave during the downpour.

(33) _________, the most annoying thing about the traffic jam is the way people react to it. Most road users ride their motorbikes on the pavement rather than (34) _________ calmly. Moreover, they constantly use their horns to hasten riders in the front, even shouting at them from time to time.