2. Which of the following best describes the theme of the passage? a. The agricultural revolution changed human food preferences.
b. Some plants today are similar to their ancestors.
c. Farming replaced hunting and gathering.
d. Agricultural communities developed from hunter-gatherer communities, and the
practice of agriculture introduced new environmental problems.

The equation below shows a chemical reaction. a + b + heat —> c + d according to the law of conservation of energy, which statement is true? a. the reactants absorb heat because they have less energy than the products. b. the products release heat because they have more energy than the reactants. c. the reactants generate heat because they have more energy than the products. d. the products require heat to form because they have less energy than the reactants.