At the cliff, the safety notice explicitly forbids crossing the barrier. At the library, donating a book is optional. Select all that apply: which sentences correctly restate those two facts?

الشرح

Visitors mustn't cross the barrier correctly restates the explicit prohibition, whereas don't have to would only remove a need to cross. The library sentence correctly presents the donation as optional for new members; mustn't would wrongly turn that voluntary action into a ban.