Camels have been known to store their food in their body which ____________ humps.

The sentence is of present perfect tense. It is to be noted then that the verbs to be used in the sentence should be grammatically correct. Options 1 and 3 are eliminated because the verb “became” is used which is past participle form of verb and its use is grammatically incorrect.  Option 4 is also eliminated because “+ing form of verb” is usually used in present tense, present continuous tense or present perfect continuous tense and not with perfect tenses.

Hence, the correct answer is option 2.