．________boys and girls in that school are almost equal, of which both of the headmasters are proud.

A．A number of

B．The numbers of

C．Numbers of

D．The number of

生态系统是指在一定空间内生物的成分和非生物的成分通过物质循环和能量流动相互作用、互相依存而构成的一个生态学结构单位。