Rewrite these sentences, beginning as shown, so that the meaning stays the same

VI. Rewrite these sentences, beginning as shown, so that the meaning stays the same.
1. I don't buy it because I don't have enough money.
→ ....................................................................................
2. I didn't buy it because I didn't have enough money.
→ ..........................................................................................................
3. There was a test yesterday. I didn't know that, so I didn't study for it.
→ ..............................................................................................................
4. I'm busy right now, so I can't help you.
→ ...................................................................................................
5. He's very thin, that's why he feels so cold.
→ .......................................................................................