9. We oughtn’t (work)__to work____ lazily and carelessly.   

10. She used (be)__to be____ my next-door neighbor in Hue.   

11. Minh’s father (teach)__taught____ him how to ride a bike when he was seven. 

In my opinion, the best leisure activity for teenagers is play sports. Firstly, you must choose one of your favourite sports. You can choose individual sports or team sports. but I would like to advise you that you should play team sports because team sports help you connect to friends, confident more and funnier than play individual sports. Secondly, you need to find friends have the same interests to play this sport. Thirdly, you have to organise the sport in a suitable location like where is large, cool and the weather is good. Also, you can invite your friends to your backyard house. For these reasons, I believe sports can replace play computer games for many hours a day. Instead, it also improves your health and your concentration, too!