氨基酸跨膜转运进入一般细胞的形式为( )。
A．单纯扩散
B．通道转运
C．泵转运
D．载体转运
E．吞饮
参考答案：D
Not until I read your letter ________ the true state of the affairs.
A．did I understand
B．had I understood
C．I understood
D．I had understood
