English文法 一些問題....請幫幫我

No need to make this question so complicated. It is just a problem of comparative and superlative.

Adjective / Adverb Comparative Superlative
Beautiful more beautiful most beautiful
Quick quicker quickest


So when you are comparing 2 things or persons, you use comparative.
When you are comparing more than 2 things or persons, you use superlative.
And this is the reason why sentence B is wrong, because you should use a superlative – most challenging because you are comparing more than 2 sports, you are comparing with ALL sports.

呢個問題同句意無關，三種運動都可以 challenging。
問題係形容詞o既用法：
１．成為句子中 subject o既 complement，如：
I am happy. 句子中有 object，happy 就係 subject complement，用 verb to be 帶出。你o既問題中，A 同 C 都係呢個情況。
２．用於形容一個名詞，放於名詞之前，如：
He is a naughty boy. 留意，名詞本身有 article（冠詞，即係 a / an / the），加o左形容詞，冠詞唔會無o左。
B o個句之中，"we think bungee-jumping is challenging sport of all" 就係冇左個冠詞，而因為句子有 "of all"，即係其實係將 bungee jumping 同其他運動比較，其中以佢最為有挑戰性，所以要用比較級中最高級o既 the most。
如果要改正呢句，就要寫成："we think bungee-jumping is the most challenging sport of all"

We think bungee-jumping is the most challenging sport of all.
It means among all the different kinds of sport, bungee-jumping is the most challenging.