決定參加 (某活動、計畫等)；決定加入 (某組織、團體成為會員)
If you want them to notify you of updates, you have to opt in.
opt into +
I opted into the scheme.
We palled up when I started working with her.
part with +
I found it very hard to part with my old CDs when I digitized my collection.
pass * back +
I felt awful when the teacher started to pass back the exam papers.