Rasha Assem posted:
May I use your calculator? – Of course, you ……… ; I don’t need it now.
a may b can’t c can d may not
The answer given is 'c'. I would like to know why 'a' isn't correct?
Answers (a) and (c) are both correct, regardless of what the textbook says. It actually makes sense to use a modal in the response that mirrors the modal used in the question. In other words, I find (a) to be a better answer than (c).
Incidentally, "can" can be used to ask for permission and to give someone permission. In case you're skeptical, I recommend that you watch this short video on the matter. Geoffrey Pullum is one of the greatest grammarians now living.
Also, for what it's worth, in real life the first sentence of the response could simply end with "Of course", which means "Yes" and implies that the speaker is giving permission. Adding "you may/can" is OK but redundant.