who / how / where / what

Question

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;

1. We think him to be nice. --> an adjective "nice" can be replaced with "how."
2. We think him to be a doctor. --> a noun "a doctor" can be replaced with "what."
3. 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?

Answer 1

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.