下列说法中正确的是

A．一个物体能不能看做质点是由它的大小决定

B．速率就是瞬时速度的大小

C．速度可以描述物体位置变化的快慢

D．牛顿最早用科学方法研究了自由落体运动

Leaders of the BRIC countries-----Brazil, Russia, India and China----_______their second summit on Friday. President Hu Jintao then returned home to help direct relief work ______the deadly earthquake in Qinhai.

A．left, to follow

B．concluded, following

C．had left, following

D．had concluded, followed