1,you mustn't be late if you want---------------------------

you mustn't be late if you want to catch up with the early bus (赶上早班公共汽车)
2,I'll tell him about it when he comes to see my (他来看我) 时间状语从句,要用一般现在时态代替一般将来时态
3,don't talk to me when I'm doing my homework (作业)
4,you must read it again before you do the exercise (做这道练习题)
5,he must be very tired after he walked for three hours (3小时)
6,you need help if you can't repair the radio(修理这台电视机)
7,they go to the farm to help with the rice harvest when the farmers are busy (很忙)