大多数氨基酸的合成是多步反应的产物，但20种标准氨基酸中有3种可以通过中枢代谢途径中的糖类代谢物经简单转氨基合成。

（a）写出这三个转氨基反应的方程式。

（b）这些氨基酸中有一种也能直接通过还原氨基化合成，写出此反应的方程式。

Another critical factor that plays a part in susceptibility to colds is age. A study done by the University of Michigan School of Public Health revealed particulars that seem to hold true for the general population. Infants are the most cold-ridden group, averaging more than six colds in their first year. Boys have more colds than girls up to age three. After the age of three, girls are more susceptible than boys, and teenage girls average three colds a year to boys’ two.
The general incidence of colds continues to decline into maturity. Elderly people who are in good health have as few as one or two colds annually. One exception is found among people in their twenties, especially women, who show a rise in cold infections, because people in this age group are most likely to have young children. Adults who delay having children until their thirties and forties 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 cramped quarters than those typically occupied by wealthier people, and crowding increases the opportunities for the cold virus to travel from person to person. Low income may also adversely influence diet. The degree to which poor nutrition affects susceptibility to colds is not yet clearly established, but an inadequate diet is suspected of lowering resistance generally.

Which of the following conclusions does information in Paragraph 2 support

A．Men are more susceptible to colds than women.
B．Women having babies are more susceptible to colds.
C．People who live in a cold climate have more colds than those who live in a warm one.
D．People who don’t have children are more susceptible to colds than those who do in their thirties or forties.