THE CORRECT ANSWER IS (E). THE ORIGINAL VERSION IS REDUNDANT IN IT...
11. The correct answer is (E). The original version is redundant in its use of job twice.
Also, at times is not idiomatic here. (Either sometimes or occasionally would have been
correct.) Choice (E) corrects both problems. So does choice (D), but using the word some
twice sounds clumsy and alters the sentence’s meaning—by going too far in limiting the
situations in which a demonstration is requested.