Complete the exchanges with the correct modal verbs

• can't
• has to
• might have
• gone
• mustn't
• need
• can
• should
• wasn't able to

1. — Could Tom help with my English homework?
   — Sorry, he [ ]. He [ ] tidy his room first.
2. — Where's Sam?
   — I don't know. He
   [ ] already [ ] to university.
3. — Why are we driving so slowly?
   — There is a sign here. I
   [ ] drive faster than 50 km per hour.
4. — I
   [ ] to buy an envelope to post this letter.
   — Look over there! We[ ] find it in that post office.
5. — I need your advice. I can't get access to this site. 
   — You [ ] register first.
6. — How was your exam yesterday?
   — Not good. I
   [ ] pass it.