Ответ:
1. It is necessary for you to have a computer password.
You need to have a computer password.
2. It isn't necessary to stay in the exam hall after you have completed the test.
You neednt stay in the exam hall after you have completed the test.
3. I advise you to seek help if you are having problems understanding something.
You ought to seek help if you are having problems understanding something.
4. Nia is a very well-behaved child. I doubt that she was nasty to the other children.
Nia is a very well-behaved child. She
couldn't have been nasty to the other children.
5. Richard has the ability to solve maths problems very quickly.
Richard can solve maths problems very quickly.
6. Students are obliged to be on time for class.
Students
must be on time for class.