please help. im terrible with clauses. i have narrowed it down to a/b because they begin with a relative pronoun. but neither of them end with the question (What kind? How many? or Which one?) can someone please explain the correct answer and why?
11 which clause in this sentence is used as an adjective
When Beowulf arrived, the danes welcomed him, for they desperately needed someone who could stop Grendel.
A when Beowulf arrived
B the danes welcomed him
C they desperately needed someone
D who could stop Grendel

Question

please help. im terrible with clauses. i have narrowed it down to a/b because they begin with a relative pronoun. but neither of them end with the question (What kind? How many? or Which one?) can someone please explain the correct answer and why? 
11 which clause in this sentence is used as an adjective
When Beowulf arrived, the danes welcomed him, for they desperately needed someone who could stop Grendel.
A when Beowulf arrived
B the danes welcomed him
C they desperately needed someone 
D who could stop Grendel