question: What sentence would provide a factual answer to this question: "When the scientist finally completed his new invention he thanked his"

answer: scientists make observations

question: What sentence would provide a factual answer to this question: "Ways to create reuseable energy could be:"

answer: a solar panel converts sunlight into electricity

question: What sentence would provide a factual answer to this question: "If someone wants to use a natural gas in order to assist something necessary, they can"

answer:
natural gas is a source of heat by burning