Q:

who / how / where / what

There was a question on the test that I was not sure which option was correct.
The question is

Fill in the blank choosing the most appropriate word.

Duke is not (   ) we think him to be.

who / how / where / what

It seems to me that "how", "where", "what" could go into the blank,
as I thought we could say;

We think him to be nice.
--> an adjective "nice" can be replaced with "how."
We think him to be a doctor.
--> a noun "a doctor" can be replaced with "what."
We think him to be at home.
--> an adverbial phrase "at home" can be replaced with "where."

And "who" sounds funny in an ordinary situation because we already know it is Duke.
I chose "what" in the end.
Will someone please explain to me which one is correct, together with some explanation?

A:

All of these could be correct depending on context. Your three examples show a good understanding of the different meanings. You could also say:

Duke is not who we think him to be. (We thought we knew Duke but that is not his real name, he is a spy.)

I suspect the question was testing your knowledge of the correct relative pronoun:

The man who ... The table which ... The place where ...

If that's the case it is a poorly worded question: you have demonstrated that any of the words are acceptable.

