If some animals communicate through barks and snarls, then some animals communicate through what? Answer choices: - chemical reaction - eating quietly - vibrating quickly - being silent - chemical changes - hormones - barks and snarls - chemical messengers
barks and snarls

If greenhouse gas concentrations in the air have increased over the last decade dramatically, then what have increased over the last decade dramatically? Answer choices: - gasoline concentrations - Warm air moving into cold air - Greenhouse gases - treehouse gas concentrations - movements in the earth's crust - concentrated orange juices - genetic diversity - greenhouse gas concentrations
greenhouse gas concentrations

If humans require water for survival, then what requires water for survival? Answer choices: - bamboo - air - pigeons - omnivores - oxygen - humans - books - bushes
humans