A total of 548 students fell ill ______ consuming milk and biscuits in schools in Northwest China's Qinghai province on Wednesday, local authorities said.

A．before

B．when

C．after

D．while

任何人到加油站检查要求打开投币式保险箱时，均要打电话给公司财务部指定的人员，核实检查人员身份，否则不得打开。