Modal verb

Hello,

1 Could I come back and stay the next time I have a treatment? (polite request )
2.Radhika can sing very well. (ability)
3.You may leave the room after the lecture is over. (permission)
4.He will collect the books in the evening. (future tense)
5.This medicine may/might cure the patient. (possibility)
6.Inspite of being weak, he could win the wrestling match (ability)
7.The police might be able to find the thief. (remote possibility)
8.They would sit in the cafeteria every evening. (past habit)
9.You must follow the rules of the institution. (compulsion)
10. Living in such filthy conditions must be difficult. (guess/conjecture)
11.You mustn't (needn’t, mustn’t, won’t) light a match, the room is full of gass.

I have to fill up the gaps with a suitable modal verb as per the instruction given for each sentence. The instruction are given in brackets against each sentence. I have filled up the gaps with the modal verbs which are bold letters.

Could anyone check my answers?

Thanks.