How do human beings contribute to the phosphorus and sulfur cycles?
a. deforestation

b. planting trees and shrubs

c. adding chemical fertilizers to the soil

d. introducing fish species to ponds and lakes

All living organisms are composed of a. only one cell. b. at least 100 cells. c. at least three cells. d. one or more cells.

Which of the following must be true for a fossil organism to be useful as an index fossil? a. the fossil organism must be widespread geographically. b. the fossil organism must be abundant. c. the fossil organism must be limited to a short span of geologic time. d. all of the above.

Why are some places regularly warmer or cooler than others in a given month