This approach, more expensive than the basic one, provides us with considerably more usage flexibility.
A. as
B. since
C. while
D. if
网友回答
A. as
B. since
(答案→)C. while
D. if
解析：考查连词。A.as因为，一边．．．一边，尽管（要用倒装）B. since既然，自从．．．以来C.ｗhile当．．．时候，尽管D.if如果。句意：这种方法，尽管比基本方法更昂贵，但我们提供了更多的使用灵活性。故选Ｃ