The children were playing games on the playground school uniforms.A. all of them woreB.

问题补充：

The children were playing games on the playground, school uniforms.

A. all of them wore

B. all wearing

C. all of whom wearing

D. all were wearing

答案：

A. all of them wore

(答案→)B. all wearing

C. all of whom wearing

D. all were wearing

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。