The administration has increased the number of fines for mining safety violations as part of their campaign to protect miners.

(A)has increased the number of fines for mining safety violations as part of their
(B)have increased the number of fines for mining safety violations as part of their
(C)has increased the number of fines for mining safety violations as part of its
(D)has increased the amount of fines for mining safety violations as part of its
(E)have increased the amount of fines for mining safety violations as part of their

I got this one from Manhattan. I do not agree with the official explanation.

[spoiler]OA : C[/spoiler]