2. an example of a predator-prey relationship would be a. tree-water b. cow-grass c. hawk-mouse d. tick-dog 3. which of the following gasses is the result of life forms being present on earth? a. oxygen b. carbon dioxide c. water vapor 4.a. global warming b. absence of predators c. depletion of the ozone layer d. brush fires that destroyed the food supply 5.a. organs used in breathing b. food source c. method of reproduction d. pattern of movement 6. which of the following statements is true about organisms that are producers? a. they use energy from the sun to make food. b. they absorb energy from a host animal. c. they get energy from eating living plants. d. they get energy by breaking down dead plants and animals.