Among the different types of scientific knowledge are likely to be modified or discarded most frequently. long ago, in the 1600s, scientists discarded the phlogiston theory because

line 1. hypotheses, laws, theories
line 2. scientists wanted to explain things differently, new evidence didn’t support it, it was too old and needed to be replaced

During a scientific study a hypotheses is generally modified or discarded

so for first blank the answer is hypotheses

Now in case of phlogiston theory it was assumed that when a substance catches fire it evolve certain substances known as phlogiston which was later on discarded as there is no such particle. Infact a substane undergoing oxidation may gain weight

Hence in second blank the answer is new evidence didn’t support it,