A) I am sure he isn't from Cyprus. b) Perhaps he was reading.
c) Perhaps Devkota wrote that poem.
d) Obviously, she passed the entrance.

This question is incomplete. I've found the complete question online. It is the following:

5. Change the sentences below using must, can’t and might\may, whichever is correct.

For example: perhaps he was tired.

                      He may have been tired.

a) I am sure he isn’t from Cyprus.

b) Perhaps he was reading.

c) Perhaps Devkota wrote that poem.

d) Obviously, she passed the entrance.

a) He can't be from Cyprus.

b) He might have been reading.

c) Devkota may have written that poem.

d) She must have passed the exam.

Explanation:

The options are the following:

must - indicates an obligation or a conclusion we reach with a high degree of certainty. For instance: James is never late. Something must have happened, otherwise he would have arrived already.

can’t - indicates lack of skill to do something or impossibility of something happening. For example: She can't have taken the bus. She had no money with her.

might\may - indicate some degree of probability and possibility, but not a high one. For instance: I might call you tomorrow, but I'm not sure. / He may have forgotten about the meeting. Let's give him a call.

Having the explanation above in mind, we can

a) He can't be from Cyprus.

b) He might have been reading.

c) Devkota may have written that poem.

d) She must have passed the exam.

yes yes it does !