Change the tense of the following:
1. They often play cards.
a) When I saw them,…. When I saw them, they were playing cards……………
b) for two hours …….. They have been playing cards for two hours. ………….
c) While we were studying maths, ………………………………………………..
d) three hours ago …………………………………………………………..
e) on Saturday nights ………………………………………………………….
f) at the moment