胃泌素产生于（）。
A．壁细胞
B．主细胞
C．粘液细胞
D．G细胞
E．肥大细胞
参考答案：D
______ to computer games, he had no time to go over his lessons. As a result, he failed in all subjects.
A．Addicting
B．Being addicted
C．Having addicted
D．Addicted
简述中国警察道德发展的规律。
