You want to repeat Mendel's experiments with an eighth trial. You choose flower color. Pea plants have flowers that are white or colored. To get a pure-bred colored flower plant you start with a colored flower plant.
What should you do next?
This is a pure-bred colored flower plant.
Self-fertilize this plant. If all the flowers of the next generation are colored, the plant was pure-bred.
Cross-fertilize this plant with a colored flower plant.
Cross-fertilize this plant with a white flower plant.