—Could you tell me             at the meeting?

—Sorry, I don't know. I didn't go to the meeting that day. [ ]

A. what does he say

B. what he says

C. what he said

D. what did he say

杆长为2a的AB杆置于半径为R的固定半圆槽内，C为AB杆的重心，图示为AB杆的平衡位置，则重力P对圆槽O点之矩，即m_o（P）=（）。

A．A

B．B

C．C

D．D