Ex3: Put "should/ shouldn't/ Have to/ has to / had to" into these senteces:     
1.We.........do volunteer work to help homeless people and street children.     
2.You........smoke or drink alcohol because these things are bad your health.     
3.Marry........wear a uniform when going to school. It's the rule at her school.     
4.I don't........clean the kitchen because my mom does this every day.     
5.In the past, children........go to school on foot.     
6.Do you think you........go on a picnic with your family this weekend?     
7.I think i........study harder to get good marks.     
8.He........finish this plan to day.     
9.She........do a lot of work yesterday.     
10.You........drive too fast because it's dangerous.

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