Which nutrient plays an essential role in muscle-building?

Plants need which gas to perform photosynthesis?

Earth is surrounded by layers of gases collectively called the _____.

Which system of the body controls the senses?

Which is the largest animal on earth?

Which is the strongest sense in a dog?

What are animals, which eat both plants and animals, called?

Which is the closest planet to the sun?

Which pigment gives the leaves its green color?