advertisements are of great help, I don’t think we should entirely rely on them.
A. Because
B. Since
C. Once
D. While
网友回答
A. Because
B. Since
C. Once
(答案→)D. While
解析：考查连词：A. Because因为 B. Since自从，既然， C. Once 一旦D. While虽然，然而，当…时候，句意：虽然广告对我们很有帮助，但我想我们不该完全依赖它们。while表示虽然，有转折的意思。选D。