Nitrogen is used to produce

a. proteins

b. DNA

c. both proteins & DNA

The transport tubes for food coming down the plants are called?

Diagram of the evolution of land plants?

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