设T为n(n≥3)阶无向树，T有几条割边( )
A．n条
B．n-2条
C．n-1条
D．没有
参考答案：C
She _______________ her homework last night. [ ]
A. didn't
B. doesn't
C. didn't do
D. doesn't do
运动负荷试验时，极量心率粗略计算法为（）
A.190-年龄
B.200-年龄
C.210-年龄
D.220-年龄
E.250-年龄
