Which best explains how and why scientific knowledge is continually expanded and improved?

the scientific process flows in one direction and finds only facts that support a scientist’s original idea.
the scientific process is cyclical so that new facts inspire questions that lead to new studies.
once explanations are found to be true, they do not need to be questioned; then scientists can stop studying the topic.
once facts are found through experiments and observations, other scientists do not need to repeat the experiments.