on "can"/"ability"

[maqiuming.q]

Hi, In the idioms chapter, the problems set, #5.
Unlike humans and guinea pigs, most mammals _______ synthesizing Vitamin C from glucose, a simple sugar.
1. Why in the blanks "have the ability of " is wrong according to the standard answer?
2. Why "have the capability of"/"are able to"/"have the ability to" are suspected although grammatically correct? Is it due to concise rule?

Thanks a lot for helping me in solving my puzzle!

[RonPurewal]

Hi, In the idioms chapter, the problems set, #5.
Unlike humans and guinea pigs, most mammals _______ synthesizing Vitamin C from glucose, a simple sugar.
1. Why in the blanks "have the ability of " is wrong according to the standard answer?

... because it's an idiom. the whole point of idioms is that they don't have logical explanations -- they just are what they are.
you don't "have the ability of ___ING" because, well, you just don't. (you "have the ability to ____")

2. Why "have the capability of"/"are able to"/"have the ability to" are suspected although grammatically correct? Is it due to concise rule?

the first of these is a bit wordy, yes -- but, remember, "wordiness" should always be a relative decision, not an absolute one.
i.e., you don't ever want to look at one choice and decide whether it's "wordy", all by itself -- that's much too hard (and much too arbitrary). instead, just compare the diction in the different choices; if you notice one choice that's substantially more wordy than another, be suspicious of it.

the second and third of these are not just "suspicious"; they are completely wrong. (you can't "be able to ____ING", although you can be able to _____. same for the latter one.)