The author warns the reader to be cautious when ________.

A．products are more expensive in the U.S. than anywhere else
B．credit cards are often used illegally
C．products very often do not perform as advertised
D．most Americans like to buy what they cannot afford

A．the brand names of products they buy regularly
B．why they purchase certain products
C．the current interest rates on savings accounts.
D．where to buy cheaper things