take part in, join和join in 都有“参加”的意思,可是它们之间还有很大的区别：
take part in
take part in 意为“参加,参与（某事物或某活动,如movement, revolution, meeting, conference, conversation, war等）”.例如：
Switzerland didn't take part in this war. 瑞士没有参加这次战争.
How many countries will take part in the World Cup? 有多少个国家要参加世界杯?
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.
