In spite of what its critics say, the new, expensive artificial kidney implant is a boon to modern medicine. These critics should remember that the first heart transplants stimulated an enormous amount of beneficial medical research, even though the transplant technique was later rejected in favor of less invasive surgical procedures.

The author defends the artificial kidney implant against the critics by

Analysis of the argument: The author says that irrespective of what critics say about Kidney implant (that it's expensive etc), it's beneficial to modern medicine.

Then the author explains how it's beneficial by giving an analogy of heart transplant.

Therefore, the option which is implying this sort of reasoning would be the correct answer.

Let's look at the options:

(A) attacking her opponents' method of circular reasoning...................It's not a circular fallacy (wrong logic)

(B) implying an analogy between the benefits of the artificial kidney implant and the benefits of the early heart transplants.......................This matches with our reasoning. Keep it.

(C) pointing out a contradiction implicit in their criticism of the implant's high cost......................The argument implies that critics criticized artificial heart transplant not because of high cost but because of the method of the transplant. Therefore, wrong.

(D) criticizing the professional objectivity of her opponents rather than their claim..................Author is not talking about objectivity.

(E) implying an analogy between the critics' opposition to the artificial kidney implant and their opposition to the early heart transplants................Trap answer choice. Author is saying kidney implant will be beneficial to modern medicine just like artificial hear transplant has become.
Also, the argument says that the artificial heart transplant was rejected later by critics.