When did your brother the army?A.join B. join in C. take part in

问题补充：

When did your brother the army?

A.join B. join in C. take part in

答案：

解析：根据语境可知此句的含义是你哥哥什么时候参加的军队？the army是个组织故用谓语动词join。而没有join in这种表达方式。Take part in也表示参加其后常跟活动。故选A。