all of you are top students only one will be chosen for the coming competition.A. While

问题补充：

all of you are top students, only one will be chosen for the coming competition.

A. While

B. Since

C. If

D. As

答案：

(答案→)A. While

B. Since

C. If

D. As

解析：句意：尽管你们都是很优秀的学生，但是将只有一个学生将被选出来参加竞赛。While：尽管，当...时候 Since：既然，因为 If：是否 As：由于，随着。句意前后有转折关系，所以用while引导让步状语从句。故选A。