Answer :
B. Who is used as a subject and C. Whom is used as an object are the correct answers when it comes to determining whether to use who or whom in a relative clause.
Answer:
Option B and C
Explanation:
In case of relative clause , the object and subject of the sentence is determined by looking at the state of the verb.
The best and easiest way to do so is by asking questions with respect to the verb
a) The answer obtained in lieu to the question asked as "who" is doing the action defined by the verb in any sentence is the subject of the sentence
b)The answer obtained in lieu to the question asked as upon "whom" is this action being done as defined by the verb in any sentence is the object of the sentence
Hence, option B and C are correct