That's funny, my gut tells me the exact opposite.
I'm not surprised, and BTW, neither of you got all correct (according to CMOS, that is). They say the correct answers are that (a) and (b) are incorrect, but (c) is correct.
I think my test has shown that some ways these pronouns are used in sentences make it very tricky to work out what is "correct".
Are you ready to become totally confused? Here is what CMOS 5.63 says (with my bold font for emphasis):
'Who' and 'whoever' are the nominative forms - used as subjects [Whoever said that?] or predicate nominatives [It was who?].
'Whom' and 'whomever' are the objective forms - used as the object of a verb [You called whom?] or object of a preposition [To whom are you referring?].
Three problems arise with determining the correct case:
- First, because the words are so often found in the inverted syntax of an interrogative sentence, their true function in the sentence can be hard to see unless one sorts the words into standard subject–verb–object syntax. In this example, sorting the syntax into "I should say who is calling" makes the case easier to determine:
WRONG: Whom should I say is calling?
RIGHT: Who should I say is calling?
- Second, determining the proper case can be confusing when the pronoun serves a function (say, nominative) in a clause that itself serves a different function (say, objective) in the main sentence. It is the pronoun's function in its clause that determines its case. In the first example below, the entire clause 'whoever will listen' is the object of the preposition 'to'. But in the clause itself, 'whoever' serves as the subject, and that function determines its case. Similarly, in the second sentence 'whomever' is the object of 'choose' in the clause 'whomever you choose', so it must be in the objective case even though the clause itself serves as the subject of the sentence.
WRONG: I'll talk to whomever will listen.
RIGHT: I'll talk to whoever will listen.
WRONG: Whoever you choose will suit me.
RIGHT: Whomever you choose will suit me.
- As the second example above shows, a further distraction can arise when the 'who' clause contains a nested clause, typically of attribution or identification (here, 'you choose').
I hear moans of, "WTF is a predicate nominative?"
I'll start a new thread called 'What is a Predicate' attempting to explain that, but basically they are the little beasties which cause most of the problems people have when deciding which personal pronouns to use. I'm sorry, but the opening post for that will include about four quotes from the dreaded CMOS. I have looked for, but haven't found, any adequate explanations elsewhere.
Perhaps now, with what the rules say about what is "correct" all settled (WTF?), we can now move on to when and why people use these incorrectly, and what that means for out choices as authors.