— I think travelling by train is more comfortable than travelling by plane.

—_________. In my opinion, travelling by plane is more comfortable.

A．I agree with you

B．I couldn’t agree more

C．You’re right

D．I’m afraid it isn’t

某次军事演习中，一架无人机停在空中对三个地面目标点进行侦察。已知三个目标点在地面上的连线为直角三角形，两个点之间的最远距离为600米。问无人机与三个点同时保持500米距离时，其飞行高度为（）米？

A.500

B.600

C.300

D.400