Which Two Ideas Are at the Heart of the Scientific

Which two ideas are at the heart of the scientific method?

A) all knowledge is final, and not subject to refutation
B) most knowledge is provisional, but cherished beliefs are not subject to refutation
C) knowledge obtained in a scientific way is final, and not subject to refutation
D) all knowledge is provisional, and subject to refutation
E) all knowledge should be tested scientifically, then it is no longer subject to refutation