1,How many athletes attended the last olympic games?
2,Please tell all the children to join in the game.
3,My father joined the army at eighteen .
4,Do you know when she join the party?
5,How many years have you been in the communist youth league?
6,If anyone of you pick up the watch,please hand in to me.
这里考察的是join,join in,take part in ,attend
http://wenku.baidu.com/view/865eaf69a45177232f60a273.htmljoin是"加入"的意思
而"join in"是"参加"的意思
例如:参加党(join the Party)
还有"take part in"也是"参加"的意思
例如:参加歌咏小组(take part in the singing group)
还有"enter for"是"报名参加"的意思
例如:报名参加数学竞赛(enter for the maths contest)
当join和join in当“参加”讲时。
join表示参加某一团体、组织、机构，并作为其中一员（如：入党、入团、入会、参军等）
e.g.He joined the Labour Party/this company in 1999.
他1999年加入了工党/这家公司。
join in: to take part in an activity 参加(活动)
e.g.We all joined in the singing.我们大家一起唱歌。
另外：join也有to take part in an activity的意思
但join后接的名词似乎更加抽象
e.g.Come on in and join the fun!快进来一起完吧！
enter for 是报名参加的意思。（enter这个词有登记的意思）
e.g.He entered himself for the exam.
Attend
attend39 vt.①出席，参加②照顾，护理 vi.(与to连用)①专心于，致力于②照顾
经典例句After sleepless nights and long hours of backbreaking work, the prisoners were forced outside to attend roll-calls which lasted for hours.在无数不眠之夜和长时间高强度工作之后，囚犯们还被迫进行几小时的露天点名。
词汇辨析join, take part in, attend, enter：
join 参加，加入，成为……的一员；
take part in 参与，参加某种活动；
attend 出席，参加，定期去（某处）；
enter 加入，开始从事；开始参加。