help me solve this, it's a part of an english test, i can't understand the grammar of this sentence.
There could be many mechanisms working together that _(12)_us in choosing genetically similar friends_(13)_”functional Kinship” of being friends with_(14)_!
12. [A] drive [B] observe [C] confuse [D]limit
13. [A] according to [B] rather than [C] regardless of [D] along with
14. [A] chances [B]responses [C]missions [D]benefits