The best answer is b - experiment.
An organized process that is used to gather and analyze observations and test a hypothesis is an experiment.
An experiment is the fourth step in scientific method after observation, question and hypothesis.
An experiment is a test that is carried out under controlled conditions with the purpose of demonstrating a known truth, determine the efficacy of a yet untried thing or to examine the validity of a hypothesis.
A hypothesis is a proposed solution for an occurrence that is still unexplained and which does not fit in current accepted scientific theory.
