$\textrm{1. We mustn't drop litter in the street.}$

$\textrm{2. All drivers must have a driving license.}$

$\textrm{3. You mustn't smoke in this area.}$

$\textrm{4. You mustn't use the mobile phone during the exam.}$

$\textrm{5. Students mustn't eat chewing gum in the class.}$

$\textrm{6. You mustn't talk on the phone in the cinema.}$

V- Complete the second sentence with no change in the meaning, using modal verb "must" or "mustn't"

1. It is wrong of us to drop litter in the street.

→ We mustn't drop litter in the street.

2. It's obligatory for all drivers to have a driving licence.

→ All drivers must have a driving license.

3. You aren't allowed to smoke in this area.

→ You mustn't smoke in this area.

4. You aren't allowed to use the mobile phone during the exam.

→ You mustn't use the mobile phone during the exam.

5. Eating chewing-gum in the class is prohibited.

→ Students mustn't eat chewing gum in the class.

6. It's forbidden to talk on the phone in the cinema.

→ You mustn't talk on the phone in the cinema.