在空间，下列命题正确的是（　　）

A．平行直线在同一平面内的射影平行或重合

B．垂直于同一平面的两条直线平行

C．垂直于同一平面的两个平面平行

D．平行于同一直线的两个平面平行

After____seemed an endless effort, the patient was finally able to carry out ___seemed a perfect normal walk.

A．that; that

B．what; what

C．it; that

D．which; it