pick up没有“从事”的意思,但有“学到;获得”的意思
例：He was picking up the skills quickly.
他正在很快地掌握技术.
take in好象也没有这个意思
词典解释：
1.让...进入;接受
The club took in a new member last week.
俱乐部上星期又吸收了一名新会员.
2.改小;改短
The dress needs to be taken
take up有从事的意思
1.开始从事
When did he take up football?
他是什么时候开始踢足球的?
2.占用;化去
The work took up all his time.
那工作花费了他所有的时间.
你可以看看http://dict.baidu.com/s?wd=take+up
http://dict.baidu.com/s?wd=take+in&tn=dict
http://dict.baidu.com/s?wd=pick+up