Use the following statements to answer this question: I. If the extent of a market is broader, it is less likely that firms in the market can influence the market price. II. In determining whether two different products belong to the same market, it is necessary to know whether the two products can be used as substitutes for each other.
选项：

A:I and II are both false.
B:I is false, and II is true.
C:I is true, and II is false.
D:I and II are both true.