2B
a)
1 will have been working (to emphasise the duration of an action up to a certain time in the future)
2 Will you be seeing (for an action which will be in progress at a stated time in the future), will have already left (for an action which will have finished before a stated time in the future)
3 will have built (for an action which will have finished before a stated time in the future), will still be working (for an action which will be in progress at a stated time in the future)
b)
This time next Sunday, I will be studying for my History test.
By the age of 25,1 will have graduated from university.
1 will have been working (to emphasise the duration of an action up to a certain time in the future)
2 Will you be seeing (for an action which will be in progress at a stated time in the future), will have already left (for an action which will have finished before a stated time in the future)
3 will have built (for an action which will have finished before a stated time in the future), will still be working (for an action which will be in progress at a stated time in the future)
b)
This time next Sunday, I will be studying for my History test.
By the age of 25,1 will have graduated from university.