Which isotope
of carbon is radioactive?

Which medullary index indicates a human hair? a. 0.653 b. 0.733 c. 0.516 d. 0.256

Using meiosis, the sporophyte produces spores that are .

When is your breathing likely to speed up? a. when your white blood cells increase b. when your cells need more energy c. when your heart cells need more carbon dioxide d. when your blood cells have too much oxygen