4. Grammar. Choose the correct answer: 1. You must / don't have to use the mobile phone on the plane. It's dangerous. 2. You have to / don't have to eat in the classroom. 3. Sasha could / couldn't read a year ago, but now he can 4. We don't have to / have to wear a school uniform. 5. You have to / don't have to run in the corridors.

Grammar Choices:

1. You mustn't use the mobile phone on the plane. It's dangerous. (Using a mobile phone on a plane is forbidden).
2. You don't have to eat in the classroom. (Eating in the classroom is usually not allowed but not strictly forbidden everywhere, so 'don't have to' implies it's not a requirement and possibly discouraged).
3. Sasha couldn't read a year ago, but now he can. (Indicates an inability in the past).
4. We have to wear a school uniform. (School uniforms are typically mandatory).
5. You don't have to run in the corridors. (Running in corridors is generally discouraged and not a requirement).

Explanation: These sentences test the use of modal verbs to express obligation, prohibition, and ability.