问题
选择题
You cannot take back your words _________ they are out of your mouth.
A．before
B．whether
C．once
D．while
答案
C
题目分析：考查连词辨析。句意：一旦话已出口，你不能收回你说的话。Take back 收回。they are out of your mouth是主句的假设条件，故选C项。
考点 : 考查连词辨析