Which one? "more fun" or "funnier"?

Hi! About “Break Down” lesson (http://www.englishbaby.com/lessons/6827/eavesdropping/break_down), grammar point.

Bachelor parties are _ _ _ than any other types of parties.

a. funniest

b. more funnier

c. more fun

I’ve taken this quiz and I failed on this (I said it was “A”). But I still don’t get it why. Ebaby says that “C” is correct (“Bachelor parties are more fun than any…”).

But when I’ve read the grammar point, I’ve found this:

“For most long adjectives, which have three or more syllables, we use more, as in, ‘Sarah is more beautiful than Martha’. With short adjectives, which have only one or two syllables, we add -er to the end of the word, as in, ‘Jacob is smarter than Ed’. For short adjectives ending in y, like “happy,” we drop the “y” and add -ier”.

So, the adjective here is “funny”. It has two syllables (it’s short) and ends with y, so, as explained before, its comparative should be somehow “funnier”. But there’s no option for that. What am I missing?

Thanks teacher!