单选题The children were playing

问题补充：

单选题Thechildrenwereplayinggamesontheplayground,________schooluniforms.A.all of them woreB.all wearingC.all of whom wearingD.all were wearing

答案：

B解析句子中没有连词，所以排除A,D；而C选项不是完整的定语从句，所以选B，用动词的ing形式。