Between (C) and (E), I will go for (E).
Here is my reasoning:
(C)- Though it seems parallel, "for decreasing the incentive" seems non-idiomatic.
(E)- Hands down, I would have gone for (E) without hesitation had it used "to call" (for parallelism). However, (E) correctly uses " to decrease the incentive". Besides, I am not able to find anything fundamentally wrong with (E) and hence will go with (E).
What is OA?
To find what you seek in the road of life, the best proverb of all is that which says:
"Leave no stone unturned."
-Edward Bulwer Lytton