1、sign up for 指“報名/申請參加...”，如：
Can I sign up for this course in advance? 我能事先申請上這一課程嗎 ?
That sounds fantastic. Where do I go to sign up for that tour? 那聽起來好極了. 我到哪裡去報名參加呢 ?
2、take part in：指“參加到 ... 活動中”，如：
We should take part in the peaceful uses of atomic energy. 我們應該參與原子能的和平應用。
They all dressed up to take part in the New Year"s party. 他們都穿上盛裝,去參加除夕晚會.
3、join in指“作為成員參加 ...”,join後可以插進直接賓語 sb.，如：
I hope that everyone will be able to join (us) in the fun. 我希望每個人都能夠加入進來，玩得開心。
He would like to join (them) in the conversation 他願意參加這種談話]
1、sign up for 指“報名/申請參加...”，如：
Can I sign up for this course in advance? 我能事先申請上這一課程嗎 ?
That sounds fantastic. Where do I go to sign up for that tour? 那聽起來好極了. 我到哪裡去報名參加呢 ?
2、take part in：指“參加到 ... 活動中”，如：
We should take part in the peaceful uses of atomic energy. 我們應該參與原子能的和平應用。
They all dressed up to take part in the New Year"s party. 他們都穿上盛裝,去參加除夕晚會.
3、join in指“作為成員參加 ...”,join後可以插進直接賓語 sb.，如：
I hope that everyone will be able to join (us) in the fun. 我希望每個人都能夠加入進來，玩得開心。
He would like to join (them) in the conversation 他願意參加這種談話]