№3
1)They've lived in the USA for six years.
2)I've been at this schoo since I was 12.
3)The UK has been in the EU for a long time.
4)Maria hasn't felt well since yesterday.
5)We've been here for an hour.
6)They haven't been to Britain since 2005.
№4
1)I've just started this exercise.
2)We've studied this grammar already.
3)The teacher hasn't arrived yet.
4)The test has just started.
5)I haven't finished this exercise yet.
6)We've already had lunch.