Pundit: Many people blame the construction of retail locations by major corporations for the decline in locally owned bookstores over the past ten years. Yet clearly, online sales of books have also played an important role in this decline. In the past ten years, sales by online retailers of books have risen sharply, and surveys of consumer behavior have indicated that many purchasers of books online, if convenient online options had not been available to them, would otherwise have purchased books at a local bookstore.
In the pundit's argument, the portion in boldface plays which of the following roles?
【选项】
It is an explanation that the argument concludes is correct.
选项是否正确？