Q: The outer layer of what anatomical structure is so tough that it keeps out most pathogens? Choices: - liver - steel - bark - skin A:
skin

Q: What property of warm air causes it to rise above cold air? Choices: - greater pressure - greater density - higher temperature - lower density A:
lower density

Q: Rubber is an example of what type of substances that do not allow electrons to move through them? Choices: - conductor - semi-conductor - solids - insulators A:
insulators

Q: What do marine autotrophs acquire in carbonic acid, its dissolved form? Choices: - silicon dioxide - chlorine dioxide - carbon monoxide - carbon dioxide A:
carbon dioxide