1.  If I (realise) how awful this job was going to be I (not accept) it.

If I HAD REALISED how awful this job was going to be I WOULD NOT (WOULDN'T) HAVE ACCEPTED it. 

2.  If Mario (pay) the 500-dollar fine he (not be) sent to prison.

If Mario HAD PAID the 500-dollar fine he WOULD NOT (WOULDN'T) HAVE BEEN SENT to prison. 

3.  If my girlfriend's passport (be) all right she (not be) arrested in Austria.

If my girlfriend's passport HAD BEEN all right she WOULD NOT (WOULDN'T) HAVE BEEN ARRESTED in Austria.

4.  A: You (know) that horse was going to win!
     B: Don't be so stupid! If I (know) I (support) him myself.

A: You KNEW that horse was going to win! B: Don't be so stupid! If I HAD KNOWN I WOULD HAVE SUPPORTED him myself.

5.  We (have) to stand all the way to the beach. If Lucy (book) seats, as I told her to do, we (have) a comfortable journey instead.

We HAD to stand all the way to the beach. If Lucy HAD BOOKED seats, as I told her to do, we WOULD HAVE HAD a comfortable journey instead.