人体重心
参考答案：人体各个环节所受地球吸引力的合力作用点。
生物圈中的动物必须直接或间接地以________为食，是生物圈中的_______。
To my great surprise, when I entered the cinema and took my seat, I found the person sitting next
to me _________ be my brother.[ ]
A. could
B. might
C. would
D. should
