I would say b and c, since unfasten and clench are basically antonyms and those answers both have antonyms
Hope this helps so 31 animals are walking towards the river right? ok so
1 rabbit + 6 elephants then If every elephant seen 2 monkeys then 6*2 is 12.
= 19 animals.
Then another 12 animals if there is a parrot for every monkey.
19+12 is 31
so your awnser is 31
