Biodiversity affects the sustainability of an ecosystem by — A. always increasing competition for limited resources within the ecosystem.
B. allowing the ecosystem to survive many changes.
C. preventing the ecosystem from surviving many changes.
D. always decreasing competition for limited resources within the ecosystem.

Why is rain likely when warm, moisture-laden air meets cold air? a) the lighter warm air will rise and cool down, causing condensation and rain. b) the cold air moves faster and pushes the warm air away, causing condensation and rain. c) the moisture in the warm air condenses on contact with the cold air, causing rain to fall. d) the cold air mixes with the warm air, reducing its temperature causing moisture to condense.