问题补充：
How long has your brother the army?
A. joined
B. taken part in
C. been
D. served in
答案：
A. joined
B. taken part in
C. been
(答案→)D. served in
解析：join和 take part in是短暂性的动词，不用在完成时态中，C选项没有介词，后面不能接the army，只能说成是has been a soldier，所以选D选项。
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