The novel, (a) which (b) explores themes of love and loss, (c) has received critical acclaim, (d) solidifying the author's reputation (e) as a literary master.
Correct: A
Since the question is referencing a noun instead of a person, the correct answer is which. 'That' is too ambiguous, 'who' implies that we are talking about a person instead of a novel and 'it' doesn't fit into the grammatical structure. Thus, (A) is correct.