To improve the quality of our products, we asked anyone ____________ had used the products for suggestions.

A．whoever

B．who

C．which

D．whichever

在城镇交通要道区域采用盖挖法施工的地铁车站，多采用（）结构。

A.拱形

B.马蹄形

C.矩形框架

D.椭圆形