4 Complete the sentences with verbs in the past progressive form.

a I ____________________ the internet when my friends called.
b She lost her keys while she ____________________ tennis in the park.
c They ____________________ in the sea when they saw a shark.
d When I saw you, you ____________________ to your teacher.
e My sister ____________________ her homework when I came home.
f When our parents came home we ____________________ a DVD.