1) i couldn't play football because
2) when i went back to the shop
3) helen was upset yesterday because
4) we got to the theatre after
5) i didn't wait for you because
6) when i arrived at the airport

a) i hadn't read your text message
b) the plane had just landed
c) i hadn't brought my boots
d) the play had started
e) they's sold all the cheap trainers
f) i hadn't remembered her birthday