send in 是词组send him/her in. 让他/她进来.send sth in 寄送某处进行处理 Send sb in 派人去处理某事这个地方是个短语 意思是 派遣 (军队或警察);例:He has asked the government to send in troops to end the fighting.他已要求政府派部队来平息那场战斗。所以,要加in 。
military,军事,泛指与军队有关的。比如:We need to keep a strong military.troops,军队,重点在军人。比如:The president visited the troops yesterday.Army,陆军。相对于 navy,air force等corps,团,军团,大概有2-4.5万人