I need help with my homework. I cannot find the answers on the internet of books and I am not a gardener. It would be greatly appreciated if you could help out with these questions:

1) Which plants prefer bases?

2) Does the pH of the soil affect the colour of the flowers? Give at least one example.

3) Which substances do gardeners add to the soil to make it:
a) more acidic?
b) more basic?

Thanks.