How and why theories change and how this contributes to continues and ongoing nature of science

There is usually some anomalous observation that doesn't seem to fit with our current understanding. Scientists assume that by working at such anomalies, they'll either disentangle them to see how they fit with the current theory or contribute to a new theory. And eventually that does happen: a new or modified theory is proposed that explains everything that the old theory explained plus other observations that didn't quite fit with the old theory. When that new or modified theory is proposed to the scientific community, over a period of time (it might take years), scientists come to understand the new theory, see why it is a superior explanation to the old theory, and eventually, accept the new theory. Theory change is a community process of feedback, experiment, observation, and communication. It usually involves interpreting existing data in new ways and incorporating those views with new results. It may depend on a single definitive experiment or observation to change people's views, or it may involve many separate studies, eventually tipping the balance of evidence in favor of the new theory. 

The answer is d.potassium