欲穷千里目更上一层楼是谁写的诗句？
参考答案：这句诗是王之涣写的
—I like biology and history.
—Why do you like ?
A .they
B. it
C. their
D. them
窦房结细胞的起搏活动是由于下列哪些因素作用的结果( )
A．K+递减性外流B．K+递减性内流C．K+递减性外流，Na+内流和Ca2+内流D．K+递减性内流，Na+外流和Ca2+外流E．K+递减性外流，Na+内流
