听力原文:A critical factor that plays a part in people's susceptibility to colds is age. T
Generally speaking, the incidents of colds continue to decline while people are growing older. Elderly people who are in good health have as few as one or two colds every year. One exception is found among people in their twenties, especially women, who show a rise in cold infections. This is because people in this age group are most likely to have young babies. Adults who delay having children until their 30s and 40s experience the same sudden increase in cold infections.
The study also found that economics plays an important role. As income increases, the frequency at which colds are reported in the family decreases. Families with the lowest income suffer about a third more colds than families at the upper end. Lower income generally forces people to live in more limited space than those occupied by rich people, and crowding will increase the possibility of cold infections.
Question :According to the passage,what is an important factor influencing people's susceptibility to cold?
(30)
A.Work.
B.Food.
C.Social status.
D.Age.