to make things thinner or sparser

• A. Sublime
• B. Repudiate
• C. Rarefy
• D. Satiate

Answer: (C)

To make things thinner or sparser is to rarefy. This verb precisely captures reducing density or concentration, such as rarefying air or a population where the substance or group becomes thinner or less dense. It comes from the idea of making something less thick or less abundant, using the root meaning thin or few and the -fy suffix to turn it into a verb. The other words don’t fit: sublime isn’t about density, repudiate means to reject, and satiate means to satisfy hunger or fullness. So rarefy is the best match.