We use​ (a)   to say that something is ​ (b)   (a negative order).

We use​ ​ (a)   or ​ (b)   to say that something is not necessary.

You ​ (a)   finish your breakfast or you will be hungry later.

I ​ (a)   leave before 8.30 or I'll be late for school.

You ​ ​ (a)   eat that bread. It's a week old!

In football, you ​ (a)   touch the ball with your hand.

You ​ (a)   visit Paris some time. It's a wonderful city.

You ​ (a)   go near the edge of the cliff. It's very dangerous.

You ​ (a)   take off your shoes if they are clean.

Students ​ (a)   turn off their mobiles during lessons or the teacher will take them away.

You ​​ (a)   go to the check-in desk if you have checked in online.

In most Arab countries, you ​ (a)   eat with your left hand. You should use your right hand.

When you're driving, you ​ (a)   stop if someone steps onto the pedestrian crossing.

We ​ (a)   waste any more time.

Jason ​ (a)   (b)   early because he's got a doctor' appointment at eight in the morning.

We ​ (a)   ​​ (b)   exams at the end of our final year at school.

You ​ (a)   ​ (b)   your parents more often. You know how much they enjoy talking to you.

Sue really ​ (a)   ​ (b)   eating so many sweets. It's bad for her teeth.

In Britain, we ​ (a)   ​ (b)   on the left.

We ​ (a)   ​ (b)   at the new Chinese restaurant in town. I've heard it's really good.

At school, we ​ (a)   ​ (b)   white shirt and a blue sweater.

We use ​ (a)   or ​ (b)   to express rules and laws.

Must and have to have very ​ (a)   meaning. However, must often expresses the feelings and ​ (b)   of the ​​ ​ (c)   .

Mustn't and don't have to do not have the same ​ (a)   .

don't have to means that something is not ​ (b)   .

mustn't means "it's ​ (c)   ".