The following questions present a sentence

问题：

The following questions present a sentence, part of which or all of which is underlined. Beneath the sentence, you will find five ways of phrasing the underlined part. The first of these repeats the original; the other four are different. If you think the original is best, choose the first answer; otherwise choose one of the others.

These questions test correctness and effectiveness of expression. In choosing your answer, follow the requirements of standard written English; that is, pay attention to grammar, choice of words, and sentence construction. Choose the answer that produces the most effective sentence; this answer should be clear and exact, without awkwardness, ambiguity, redundancy, or grammatical error.

The tremendous insight of Einstein was that the passage of time does not appear the same while standing still as it does to a person traveling at a substantial portion of the speed of light.（）

A. while standing still as it does to a person traveling

B. to a person standing still as to a person traveling

C. to a person who is standing still as a person who is traveling

D. while standing still as to traveling

E. to a person standing still as to a person who travels