At the start of act 5, the gravediggers are discussing the fact that

a: claudius has murdered hamlets father
b: laertes has returned to denmark from france
c: ophelia has apparently committed suicide
d: hamlet is only feigning madness

C: Ophelia has apparently committed suici.e is the correct answer.

Explanation:

The Tragedy of Hamlet, Prince of Denmark was written by English poet William Shakespeare and it narrates the things that happened after Hamlet's father was gone.

At the beginning of act 5, the gravediggers discuss the apparent suici.e committed by Ophelia, this can be inferred by readers when the first gravedigger said "Is she to be buried in Christian burial that/willfully seeks her own salvation?" in reference to the facts that close the previous act, where Laertes is told about her sister's death, which looks like a suici.e that is also a sin that denied her own salvation.