As a single mother of three children, she has very little time   ________    she can spare to develop her own interest.

A．when

B．that

C．which

D．what

关于蛋氨酸循环的生理意义描述错误的为

A．生成SAM
B．四氢叶酸的再生
C．一碳单位-CH₃ 的去路之一
D．叶酸的再生
E．使FH₄ -CH₃ 成为甲基的间接供体