Choose the correct option for each sentence so that it has the same meaning and the given one

1. I'm sure it is very expensive.

   It [may|must|can't] be very expensive.

2. I don't believe it's true.

   It [may|must|can't] be true.

3. I think they are at the mall, but I'm not sure.
   They [may|must|can't] be at the mall.

4. I'm sure they are staying at home.
   They [may|must|can't]be out, they [may|must|can't] be at home.

5. I don't know, they could go for a walk.
   They [may|must|can't] be outside for a walk.

6. I'm sure they don't have a dog.
   They [may|must|can't] have a dog.

7. She's not Julia. Julia's blond!
   She [may|must|can't] be Julia. Julia's blond!