Question: Q: Different isotopes of an element have different mass numbers because they have different numbers of what? Choices: - protons - electrons - nuclei - neutrons A:
Answer: neutrons

Question: Q: Many species secrete a hard external skeleton of what? Choices: - sodium bicarbonate - hydrogen carbonate - carbon dioxide - calcium carbonate A:
Answer: calcium carbonate

Question: Q: What is the main reason for weather change? Choices: - climate change - moving energy masses - seasons - moving air masses A:
Answer:
moving air masses