Underline the topic sentence of each paragraph.①Americans make no distinction in greeting friends, acquaintances, elders, or superiors. ②When Americans see close friends, casual acquaintances, teachers, or even someone they know only by sight, they are likely to say “Hi” in all cases. ③This does not mean that they have no more regard for friends than for casual acquaintances. ④It only means that “Hi” serves as a greeting for both.

A. ①
B. ②
C. ③
D. ④