$\begin{array}{I}\text{5.Mai used to go to school on foot when she was in primary school.}\\\text{6.There is often traffic jams in the rush hour in the city center.}\\\text{7.People didn't use to worry about the traffic congestion in the past.}\\\text{8.It is compulsory to wear a helmet when riding a motorbike in Vietnam.}\end{array}$
