I went to the shop (and / because / but) bought some milk.
I went to the shop and bought some milk.
He loves playing football, (and / because / but) he's not very good at it.
He loves playing football, but he's not very good at it.
I couldn't go to the party (and / because / but) I was feeling unwell.
I couldn't go to the party because I was feeling unwell.