141. Unlike transplants between identical twins, whose genetic endowment is the same, all patients receiving hearts or other organs must take antirejection drugs for the rest of their lives.

(A) Unlike transplants between identical twins, whose genetic endowment is the same

(B) Besides transplants 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（C）

(E) Other than transplants between identical twins, whose genetic endowment is the same

In A and B, the phrases beginning Unlike... and Besides... modify patients, the subject of the main clause; thus A absurdly states that Unlike transplants..., patients... must take... drugs, and B that all patients except for transplants... must take... drugs.

B用得是besides，besides有except for的意思吗？

besides是包含的，如besides Tom, we all will go to park.意思是我们和Tom都去了。

except ( for)是不包括，except for Tom, we all will go to park.意思除了Tom,我们都去了，Tom其实没有去。

我觉得besides是表示肯定的意思，就是说"两者都。。。。" 不管是OTHER THAN, EXCEPT的意思还是 : together with 的意思，都是表示"两个都"的意思。OTHER THAN, EXCEPT 看起来好像是排除否定，但是表达的意思是:除了A。。。B也。。。即：AB都具有某个性质。

而except for表示"肯定的基础上的否定".记得高中的时候老师常举的例子就是：他除了物理不好其他科目都很好。就是用except for.

个人理解！多指教！