台阶下部平盘与坡面的交线称为（）
A.坡顶线
B.坡底线
C.境界线
参考答案：B
体育课上举行拍球比赛，张强58秒拍球232下，王明62秒拍球253下．谁拍球快？为什么？
This problem is said _____ three times.
A．having discussed
B．to have been discussed
C．having been discussed
D．to have discussed
