incredulous vs sceptical

In the following multiple choice exercise:
“A lot of people are … about the benefits of nuclear power.”
A disbelieving B sceptical C incredulous D unconvincing
The answer key gives “B sceptical” as the correct answer. However, I really can’t see why “C incredulous” is incorrect here. Could somebody give me a hand with this one, please? Thanks

I feel (off hand) if you choose C you may have to put ‘in’ after it but “sceptical about sth.” is perfect.