In laboratory rats, a low dose of aspirin

[LinqingJ930]

In laboratory rats, a low dose of aspirin usually suffices to block production of thromboxane,
which is a substance that promotes blood clotting, but not seriously interfering with the
production of prostacyclin, which prevents clotting.
(A) which is a substance that promotes blood clotting, but not seriously interfering
(B) a substance that promotes blood clotting, but not seriously interfering
(C) a substance that promotes blood clotting, but does not seriously interfere
(D) which is a substance to promote blood clotting, but does not seriously interfere
(E) which is a substance that promotes blood clotting, but not a serious interference

Why chose C rather than D? It seems that D also clear conveys the meaning.

[RonPurewal]

In laboratory rats, a low dose of aspirin usually suffices to block production of thromboxane,
which is a substance that promotes blood clotting, but not seriously interfering with the
production of prostacyclin, which prevents clotting.
(A) which is a substance that promotes blood clotting, but not seriously interfering
(B) a substance that promotes blood clotting, but not seriously interfering
(C) a substance that promotes blood clotting, but does not seriously interfere
(D) which is a substance to promote blood clotting, but does not seriously interfere
(E) which is a substance that promotes blood clotting, but not a serious interference

Why chose C rather than D? It seems that D also clear conveys the meaning.

The parallel structures in C are...
promotes blood clotting
does not interfere...
This is the actual contrast that we want to point out.

The parallel structures in D are...
is a substance...
does not interfere...
Nonsense; that's not a contrast.