On the top of the mountain two towers built more than 500 years ago.A. is standingB. are s

问题补充：

On the top of the mountain two towers built more than 500 years ago.

A. is standing

B. are standing

C. stand

D. stands

答案：

A. is standing

B. are standing

(答案→)C. stand

D. stands

解析：此句是倒装句，根据句子的主语two towers，所以动词要用复数形式；而且是一种存在，所以不用现在进行时。