Answer the following question given this paragraph: 

Investigations are at the heart of science. They are how scientists add to scientific knowledge and gain a better understanding of the world. Scientific investigations produce evidence that helps answer questions. Even if the evidence cannot provide answers, it may still be useful. It may lead to new questions for investigation. As more knowledge is discovered, science advances.


Q: What methods allow scientists to add to scientific knowledge and gain a better understanding of the world?


A:
through investigations