Someone argues that you shouldn’t drink tap water because it contains hundreds of molecules of some impurity in each glass. How would you respond in defense of the water’s purity, if it indeed does contain hundreds of molecules of some impurity per glass?

(a) Impurities aren’t necessarily bad; in fact, they may be good for you.

(b) The water contains water molecules, and each water molecule is pure.

(c) There’s no defense. If the water contains impurities, it should not be drunk.

(d) Relatively speaking, a hundred molecules is practically nothing.