27. According to the rules of the library you ...... keep the books for a fortnight.
a) may b) must c) needn't d) need​

Ответ:

According to the rules of the library you "must" keep the books for a fortnight.

Объяснение: b) must

According to the rules of the library you may keep the books for a fortnight

То есть, данный ответ: may (a)