Question: Q: The surfaces of the bones at the joints are covered with a smooth layer of cartilage, which reduces what force between the bones when they move? Choices: - vibration - expulsion - gravity - friction A:
Answer: friction

Question: Q: When do weather balloons return to earth? Choices: - when the air heats up - when the timer runs out - when the air cools - when it bursts A:
Answer: when it bursts

Question: Q: How does deeper material cause convection in the mantle? Choices: - remains stable - folds - sinks then rises - rises then sinks A:
Answer:
rises then sinks