________students are playing on the playground. ______students there is at least over 100.

A．A number of; A number of

B．The number of; The number of

C．A number of; The number of

D．The number of; A number of

移动式脚手架，一般可采用金属、木料装配而成，架下装有（）。移动式脚手架必须经过（）和验收。