Fill in the blank with the most appropriate word. I asked her ___________ was on the phone.
The correct option is B who Relative pronouns have two functions- Like other pronouns they stand for a noun or pronoun placed before them and like conjunctions they join subclauses with main clause and start the adjective clause.
The relative pronouns 'who' and 'whom' are used for persons.
'Who' should be used to refer to the subject of a sentence and 'whom' should be used to refer to the object of a verb or preposition. Thus option B is the correct answer as it acts as the subject. Option C is incorrect.
'Which' is used in case of things. Thus option A is also incorrect.
'Whomever' is a compound relative used to present a more generalising idea. Thus option D is also incorrect.