Sentence Correction

For some birds the sense of smell appears to play a role in navagation, since pigeons with surgically removed olfactory nerves were found to have increased difficulties in homing.
(A) were found to have increased difficulties
(B) have been found to have increased difficulty
(c) were found to have increasing difficulty
(D) had been found to have increased difficulties
(E) Have been found to have increasing difficulties

I'm not sure why the answer is (B)- is there a difference in difficulty/difficulties and have been found/ were found?

Unlike transplants between identical twins, whose genetic endowment is the same, all patients receiving hearts or other organs must take anti-rejection durgs for the rest of their lives.
(A) Unlike the transplants between identical twins, whose genetic endowment is the same
(B) Besides the transplant involving identical twins with the same genetic endowment
(C) Unless the transplant involves identical twins, who have the same genetic endowment
(D) Aside from a transplant between identical twins with the same genetic endowment
(E) Other than transplants between identical twins, whose genetic endowment is the same

The answer is C...I chose A...isn't it whose??