?在加入

... live green & doing the right thing ? 住在绿色科技做正确的事 nebulas ? 星云 joined in ? 在加入 ...

?参与到某项活动中

... take part in 参加 joined in 参与到某项活动中 participate 参与，参加；后接介词 in ...

?答案与解析

...A．joined in; joined B．joined; been a soldier C．joined in; become a soldier D．took park in; joined in 【答案与解析】 B 题意为“我弟弟两年前参了军，当兵已有两年了”。