What is an “abstract idea,” according to Locke?

(a) The idea of an immaterial object.

(b) An idea separated from all particular circumstances and made to serve as a representative of all its kind.

(c) A rational idea which can only be formed by philosophers, not by non-philosophers (“idiots”).

(d) The idea of an object inaccessible to the senses, such as the idea of substance or the idea of God.

(e) None of the above.