In the Lesson 24, 'A skeleton in the cupboard', there is a question in the Structure section.
The question is:
The only person I have ever known ___ a skeleton in the cupboard is George Carlton.
a) he had
b) of having
c) that he has
d) to have
The only relevant content is 'The only person I know who has a skeleton in the cupboard is George Carlton, and he is very proud of the fact.'
There's no explanation about the answer. I think:
a) Wrong. There will be two subjects, 'the only person' 'he'. This is a typical error in writing.
b) I don't understand it. The word 'of' seems unnecessary here.
c) It's a that-clause and modifies 'person'. However, 'he' makes the clause fail to meet the purpose.
d) The only expression I could recall is "be known to do sth." But there's no 'be' in this opinion.
The answer is d) to have.
I don't get it. Why d is the right choice? Please explain this to me.