Generate a sentence that answers this question: "Rainbows need".

Answer: sunlight and rain can cause a rainbow

Generate a sentence that answers this question: "The population of rabbits in an area increases. That could have been caused by".

Answer: as the available water in an environment increases , the populations of organisms in that environment will increase

Generate a sentence that answers this question: "Which of these might use plants for an energy source".

Answer:
plants are a source of biofuel