冬天，双手反复摩擦，手会感到暖和；用嘴对着双手“呵气”，手也会感到暖和．前者是利______方式增加了手的内能，后者是利用______方式增加了手的内能．

For the least. American roots are no longer an easy selling point. Through much of the postwar period, US brands could play off this cachet; Levi’s ad campaigns used wholesome themes of boy-meets-girl in a heartland American setting until the early 1990s.

A．At least

B．At the least

C．At most

D．At the most