Each boy and each girl who______in finishing the task since May 1st will win 2000 dollars, if they could really make it.
【正确答案】
D
【答案解析】根据who引导的定语从句中的时间状语since May 1st可知，从句应用现在完成时，首先排除选项B、C。另外，“each／every+单数名词+and+each／every+单数名词”作主语时，谓语动词应用单数形式。故选D。