grammar A: 1
must not
grammar A: 2
has to
grammar A: 3 and 4
must - must
grammar A: 5, 6 and 7
should - don't have to - have to
grammar B: 1
have you been surfing
grammar B: 2
has been
grammar B: 3
have been coming
grammar B: 4
have you been practicing
grammar B: 5 and 6
haven't finished - has gone
grammar C: 1
didn't have to
grammar C: 2
didn't need to / didn't have to
grammar C: 3
had to
grammar C: 4
needed to / had to
grammar C: 5
didn't have to
grammar C: 6
had to
grammar C: 7
had to
