____ well known to the Irish is ____ St. Patrick was taken to Ireland as a prisoner when he was 16.

A．It, that

B．As, what

C．That, what

D．What, that

一轻杆BO，其O端用光滑铰链固定在竖直轻杆AO上，B端挂一重物，且系一细绳，细绳跨过杆顶A处的光滑小滑轮，用力F拉住，如图所示，现将细绳缓慢往左拉，使杆BO与杆AO间的夹角θ逐渐减少，则在此过程中，拉力F及杆BO所受压力的大小变化情况是

A.先减小，后变大

B.始终不变

C.F先减小，后增大

D.F始终不变