窦房结细胞动作电位0期去极化的原因是（）
A．Na+内流
B．Ca2+内流
C．Cl-内流
D．K+内流
E．K+外流
参考答案：B
（1-1/6）×（1-1/6）×（1-1/7）×（1-1/9）的值是（）。
A．1/18
B．5/9
C．1/27
D．1/54
A lessee has a 15-year capital lease requiring equal annual payments. The reduction of the total lease liability in year 6 is equal to:（）
A. 1/15 of the original lease liability.
B. the reduction of the long-term lease liability in year 6.
C. the current liability shown for the lease at the end of year 5.
