Exercício: Teste via Internet

Hi folks

I did a test on the internet, and I had some doubts. I thought that you could explain me some mistakes of mine.
So, I know the answers, but I need to know the why.
Thanks in advance!

1) The Chancelor _______________ the new wing yesterday, but it stil isn't finish.
(x) was to have opened
( ) had to open
( ) has to have opened
( ) had to have opened

2) I ...
( )ought to give up
(x)ought to have given up
( ) ought given up
( )oughted to give up

3) I have difficult ______________ English.
(x) writting
( ) to write
( ) about writing
( ) to write

4) I'd rather ...
(x) you learnt
( ) you should learn
( ) that you might learn
( ) you learn

5) If he hadn´t know the boss, he _______________ the job.
(x) wouldn't have got
( ) wouldn't get
( ) hadn't got
( ) wouldn't had got

6) It's time ____________ some work.
(x) she did
( ) for to do
( ) she would do
( ) she were to do

7) It's now 9 o'clock and the train ____________ arrive at 8:15
(x) was due to
( ) had to
( ) must
( ) is going to

You can say only the why... It' is not necessary, without you want to explain in detail.

Best regards!