应该是join,原因如下: join join意为“参加(某组织),加入(某处任职),参加到某个人群中去,从而成为其中一员”.例如: She joined a health club.她参加了一个健身俱乐部. We both joined the Labor Party.我们俩都加入了工党. join in join in sth./ doing sth.意为“参加”,后面接的宾语一般是表示竞赛、娱乐、游戏等活动的名词或V-ing.例如: Can I join in the game?我可以参加这个游戏吗? They all join in singing the song.他们一起唱这首歌.