After it has taken over the function of the disabled white blood cells, myeloid leukemia is often signaled by pain in the spleen, which may be so overworked that it triples in size.

A. After it has taken over the function of the disabled white blood cells, myeloid leukemia is often signaled by pain in the spleen, which may be so overworked that it triples in size.

B. After it has taken over the function of the disabled white blood cells, the spleen's size may be tripled by overwork and its pain be a signal of myeloid leukemia.

C. After it has taken over the function of the disabled white blood cells, overwork may cause the spleen to triple in size, and the resulting pain is often the first sign of myeloid leukemia.

D. After the spleen has taken over the function of the disabled white blood cells, it may be so overworked that it triples in size, and the resulting pain is often the first sign of myeloid leukemia.

E. After the spleen has taken over the function of the disabled white blood cells, it may have its size tripled by overwork and pain that is the first signal of myeloid leukemia.

I could narrow it down to A or D. Can anyone please tell me whats wrong A?
Basically what I understood was that it's a misplaced modifiers problem. Also, which correctly modifies spleen and it refers back to spleen.

OA later