Jack has the most common form of color blindness. What type of color blindness does he have? red-green
Blue-red
blue-yellow
blue-green
red-yellow

Which of the following is a reason why early living organisms on earth could not have survived on the surface? 1. the lack of an ozone layer 2. the lack of oxygen in the atmosphere 3. the fact that these organisms were single-celled

The earths core is made up mainly of what 2 substances? 2. like an egg, earth has a core, a layer surrounding the core, and a thin, hard outer layer. which layers of the earth match the layers of an egg?

Under which of the following circumstances would natural selection not operate on an organism