1. All the students love the principal. He is very kind. (because of)
=> All the students love the principal because of his kindness.
2. I have forgotten the tickets. I’m sorry for it. (having)
=> I am sorry for having forgotten the tickets.
3. I saw it with my own eyes. I believed it. (if)
=> If I didn't see it with my own eyes, I wouldn't believe it.
4. The house at the end of the street has been sold. It has been empty for years. (which)
=> The house at the end of the street, which has been empty for years has been sold.
5. It's a pity he doesn't take the doctor's advice. (wish)
=> I wish he took the doctor's advice.