_____,an object has positive charge when it has lost electrons.

_____,an object has positive charge when it has lost electrons.
A、That mentioned above
B、Which has been mentioned above
C、As has been mentioned above
D、What mentioned above
【正确答案】：C
【题目解析】：本题考查从句。由题干可知,本句句子主谓语齐全.因此选项应是作为句首的状语。A.That mentioned above是定语从句，排除；B.Which has been mentioned above同样是定语从句，排除；C.As has been mentioned above:是as引导的状语从句。D.What mentioned above名词性从句，排除。答案为C。