Gina is studying a cell under a powerful microscope. The cell does not contain membrane-bound organelles. Which cell is Gina most likely studying?
an animal cell
a bacterial cell
a plant cell
a protist cell

The greenhouse effect a. something that has occurred for millions of years b. an unnatural phenomenon caused by humans that maintains earths temperature range. c. the results of the differences in the angle of the suns rays d. an unnatural phenomenon that causes heat energy to be radiated back into the atmosphere