9. A good rest in bed is all you need, and drink more water.
你需要好好休息，多喝水。
还能这样说：
Remember to take a good rest and drink more water.
You should have a good rest and drink more water.
谚语：
A good winter brings a good summer.
瑞雪兆丰年。
10. Just keep the bandage dry and come back in 3 days.
保持绷带干燥就行了，3天后回来复诊。
还能这样说：
You must keep the bandage dry and return in 3 days.
Avoid the bandage being wet and come back for a re-examination 3 days later.
应用解析：
as dry as a bone 干极了;口渴极了;
go dry 颁布禁酒令;
have not a dry thread on 浑身湿透;
in the dry 没弄湿;没碰上雨
11. How long have you been like this?
你这个样子多久了?
还能这样说：
How long has it been like this?
How long has it lasted?
谚语：
Joy often comes after sorrow, like morning after night.
暮去必将朝至，苦尽常会甜来。
12. I am sure that you got the flu.
我很肯定你得了流感。
还能这样说：
Definitely you have fallen sick with flu.
I firmly believe that you had the flu.
应用解析：
be sure to 务必，一定要;
be sure of oneself 自信;满怀信心