Noonecanwalkthewirewithoutabitoffearunless

问题详情：

No one can walk the wire without a bit of fear unless ________very young.

A．having been trained  B．trained

C．to be trained  D．being trained

【回答】

B　[此句表示被动动作。]

知识点：非谓语动词

题型：选择题