Thirteen-year old Maria and her younger sister often compete holding their breath underwater. They used to be evenly matched, but lately Maria has won each contest handily. What aspect of puberty might help explain this winning streak?

What process is believed to be responsible for the formation of the grand canyon? a) diverging tectonic plates b) converging tectonic plates c) erosion over a long period of time d) caving in of the ground due to erosion

The sun a. will become a red giant within two to three million years b. is in its main sequence, which willlast thousands of years c. is in its main sequence, which will last billions of years. d. will explode as a supernova after its main sequence

How do astronomers measure the amount of dark matter in the universe