接受氨基可直接转化为丙氨酸的是（）
A、琥珀酸
B、丙酮酸
C、苹果酸
D、草酰乙酸
E、α-酮戊二酸
参考答案：B
1996+1997+1998+1999+2000+2001等于( )。
A．11986
B．11991
C．12987
D．12989
—What did John say?
—He told me that he_________ a cold for three days.[ ]
A. has caught
B. had caught
C. has had
D. had had
