The central nervous system comprises the brain, which coordinates voluntary and involuntary responses, and the spinal cord, which coordinates actions. What word best fits the the blank in the sentence above?

What causes temperature extremes in the desert

Describe how alleles and genes are related

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