理论上的双眼单视界是（）。

A.通过注视点和双眼结点的圆周

B.通过注视点，垂直于双眼平面的直线

C.通过注视点，平行于双眼平面的直线

D.只有注视点

E.以上均不是

Have you seen Jack recently? I wonder _____ with his classmates. [ ]

A. how is he getting along

B. what he is getting along

C. that he is getting along well

D. if he is getting along well