—Could you tell me_________?

—He is in the library．

A．where Simon was

B．where is Simon

C．where was Simon

D．where Simon is

如图所示，半圆玻璃砖的半径R=10cm，折射率为n=，直径AB与屏幕垂直并接触于A点。激光a以入射角i=30°射向半圆玻璃砖的圆心O，结果在水平屏幕MN上出现两个光斑。则两个光斑之间的距离

A．cm

B．cm

C．cm

D．cm