1. It would be a good idea for you to see a debt counsellor. OUGHT  
   -> You ought to see a debt counsellor.

2. It's not necessary for them to arrive before 8.30. HAVE  
   -> They don't have to arrive before 8.30.

3. I'm sure that isn't Mark who is talking to Jane as he's in London. BE  
   -> It can't be Mark who is talking to Jane as he's in London.

4. You ought to bring an umbrella today in case it rains. HAD  
   -> You had better bring an umbrella today in case it rains.

5. It's possible that Mark will be absent from today's class. MAY  
   -> Mark may be absent from today's class.

6. Jane is not answering her phone. Perhaps she is having a meeting. MAY  
   -> Jane may be having a meeting.

7. Passengers are not allowed to bring pets on the plane. MUST  
   -> Passengers must not bring pets on the plane.

8. It's impossible for that to be Johny. He's abroad. CAN'T  
   -> That can't be Johny. He's abroad.

1. It would be a good idea for you to see a debt counsellor.
   =>You ought to see a debt counsellor.

2. It's not necessary for them to arrive before 8.30.
   =>They don’t have to arrive before 8.30.

3. I'm sure that isn't Mark who is talking to Jane as he's in London.
   =>It can't be Mark who is talking to Jane as he's in London.

4. You ought to bring an umbrella today in case it rains.
   => You had better bring an umbrella today in case it rains.

5. It's possible that Mark will be absent from today's class.
   =>Mark may be absent from today's class.

6. Jane is not answering her phone. Perhaps she is having a meeting.
   => Jane is not answering her phone. She may be having a meeting.

7. Passengers are not allowed to bring pets on the plane.
  => Passengers must not bring pets on the plane.

8. It's impossible for that to be Johnny. He's abroad.
   => It can't be Johnny. He's abroad.