which or what
Jack took part in the contest and, ______ is more surprising, won the first prize.
A. what B. which
The answer is B. Is it naturally written? Does "which" refer to "won the first prize"?
I got confused for the following sentence:
Jack took part in the contest and, what's more, won the first prize.
So I chose A.
Can you point out my mistake?
Re: which or what
Only 'what' is acceptable here, since a sentential 'which' can only follow, not precede, its referent (here, the ensuing clause (he) won first prize).