The children, _____ had played the whole day long, were worn out.

A．all of what

B．all of them

C．all of whom

D．all of which

老年人骨密度的高低主要由以下哪几种因素决定（）

A.骨成熟期所能达到的峰值骨密度

B.血清碱性磷酸酶浓度

C.达到峰值后骨质丢失的速度

D.血清钙浓度

E.尿钙浓度