1.Don't get up late , or you will miss the bus.

=> If you get up late, you will miss the bus 

2. Lan stayed up late yesterday, so she is tired today.

=> Because of staying up late, she is tired today 

3.I think you shouldn't forget to do your homework .

=> If I......were you, I would not forget to do homework

4.His sister began collecting stamps when she was10.

=> His sister has.......started collect stamps when she was 10

5.The last time we met her was two weeks ago

=> We haven't....met her for 2 weeks

6.Nam would rather hang out than stay at home.

=> Nam prefers.......hang out to stay at home