What are the genotypes of gametes of a AaBb self-pollination?

What must be true for natural selection to heppen

Chloroplasts and bacteria are in size. a. similar b. at different ends of the size range c. exactly the same d. none of these

If you relate the doppler effect on sound to the color of light waves, a police car would be the color as it approaches and the color as it recedes away from the observer.