Can you keep an eye on my bag?
Keep an eye on sth 照看（照顾）某物
A: I would like to go to toilet.Can you keep an eye on my bag?
B: Of course I can.
What kind is the most durable?
when we go to shop ,we intend to buy something which can be used for long time.
May I introduce you to Dr. Johnson?
introduce sb.(sth.) to sb.介绍某人（某事）给某人。
You can use this sentence:"May I introduce you to sb",when you wanna introduce your friends to another people that you know.
Don't waste my time anymore.
When you are tired of talking with one, you could end your conversation in saying this. When someone tries to persuade you, you could use this sentence to present your steady opinion.
We can put it off till Tuesday at 9:30.
put off - 延期、拖延, 通常指会议、活动等因故不能如期举行而不得不延期，强调“有意识地延至将来某一特定时间”, 在多数情况下, 后面说明改在何时进行,这个词比
1. The meeting has been postponed to Friday.
2. Don’t put off your assignment until tomorrow.
3. Let's put this off till some other time.