The correct response is A. When greenhouse gases are high, heat flow out of the atmosphere is lower. This traps heat in the atmosphere, which raises the Earth’s temperature.
Response B is correct in that when greenhouse gases are low, heat flow out of the atmosphere is higher, which can lower the Earth’s temperature. However, it does not represent the influence of greenhouse gases on temperature directly in the same way that A does. Response C is incorrect as greenhouse gases do have a significant effect on Earth's temperature. Response D is incorrect because it includes both A and B, which suggests conflicting effects without clearly addressing the primary influence of high greenhouse gas levels.