1. Prices went up because the war broke out. (because of)
Prices went up because of the breaking out of the war
2. You must pay a lot to have such a damaged car repaired. (cost)
a damaged car repaired costs a lot
3. Perhaps Alex hasn't received my letter. (unlikely
Perhaps Alex unlikely received my letter
4. Thousands of children died of cholera last year. (death)
there were Thousands of children's death last year.
5. Not everyone realized the severity of environmental issues. (aware)
Not everyone aware of  the severity of environmental issues.