team当然是组织,老师之所以说join组织,是因为join的意思=be a member of ...组织
选A
例句：（把这些词典上例句都记住,嘿嘿保证不会再有问题）
加入,参加,成为…的一员,同…一起做某事
They joined a moving line of marchers.
他们加入了行进者的行列.
When did you join the air force?
你什么时候参加的空军部队?
His son joined the army last year.
他儿子去年入伍.
He was eighteen years old when he joined the army.
他18岁参军.
The regular troops of Baden joined the insurgents.
巴登的正规军参加到起义军方面来了.
John joined a football club a few days ago.
约翰几天前加入了一个足球俱乐部.
Mary joined a church yesterday.
玛丽昨天加入了教会.
Who persuaded you to join this society?
谁劝说你加入这个协会?
He joined the diplomatic service in 1943.
他于1943年进入外交界工作.
Soon afterwards he joined the work of the peasants association.
不久之后,他就参加了农会的工作.
He joined a flying school in Moscow.
他进了莫斯科一所飞行学校.
Come along and join the ball game.
过来和我们一块儿打球.
After a little while she joined the dancing.
过了一会儿她参加了跳舞.
Encouraged by them,old men and women also joined them.
在他们的鼓舞下,老年人和妇女也都加入了他们的行列.