This problem is said _______ three times, but he still can’t understand it.

A．to have been explaining

B．to have explained

C．having been explained

D．to have been explained

下列具有抗动脉粥样硬化作用的药物为

A．北沙参
B．麦冬
C．鹿茸
D．何首乌
E．熟地黄