单选题 Among humans, the effects of aging vary from one individual to another. The average life ______ for Americans is around 75 years, almost twice what it was in the early 190Os.

【正确答案】 C
【答案解析】(expectancy预期)。句意为：在人群中，衰老的影响因人而异。美国人的平均预期寿命大约是75岁，差不多是20世纪初期的两倍。A．spectrum光谱，B．expectation期望，期待；D．width广阔。