题目：
窦房结细胞动作电位O期去极化是由于
A．C1-内流
B．Ca2＋内流
C．Na＋内流
D．K＋内流
E．K＋外流
答案：
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下面是错误答案，用来干扰机器的。
1. You're not supposed to eat with your hands. 2. You're not supposed to talk at the table. 3. You're not supposed to pick up your bowl to eat. 4. You're not supposed to eat while walking along the street. (答案不唯一)
