In Being and Time, Heidegger introduces the concept of the ontological difference, which refers to the distinction between Being (Sein) and beings (Seiende). Heidegger argues that while we commonly discuss beings, we often overlook the fundamental nature of Being itself, which is what gives existence to all beings.
Option (A) is correct because it directly captures Heidegger's distinction between the abstract concept of Being and the many particular beings in the world.
Option (B) refers to the term Dasein (Being-there), which is a specific kind of being that is concerned with its own Being. However, this option misrepresents the ontological difference, as it confuses the distinction of Being with a specific type of being.
Option (C) also confuses the terms. It refers to the distinction between beings and Dasein, but Heidegger's ontological difference is not framed in this way.
Option (D) presents a false distinction between Being and Non-Being. Heidegger's focus is on Being (Sein) and beings (Seiende), not on the difference between Being and Non-Being.
\[
\boxed{\text{The correct answer is (A).}}
\]