The comets shed the ice that forms their glowing tails. which subject agrees with the verb forms? that tails ice comets

The verb forms in the given sentence above are the words "shed" and "forms". In these verb forms, the subjects that agree to these are comets, and ice, respectively. The verb "shed" modifies "comets" and the verb "forms" modify the word "ice". Hope this answer helps.

Ithink the answer to that would be b):

Answer (d) may increase or decrease porosity through dissolution or deposition;