The key answer of exercise 4

a)

1. a
2. b

b)

1. have; past participle
2. be; -ing form

c)

1. I'll own → own is a state verb and not usually used in the continuous form.
2. by → I'll have finished by 12 = 'at some time before and no later than 12'; I won't have finished until 12 = 'I expect to finish at 12 and no earlier.' (Notice that for this meaning we use a negative verb.)

d)

1. I’ll have left home.
2. They won't have finished.
3. We’ll be living in Spain.
4. It'll be snowing.