The Surface of the Sun Appears Sharp When We Look

The surface of the Sun appears sharp when we look at it in visible light because

A) the photosphere is cooler than the layers below it.
B) the photosphere is thin compared with the other layers in the Sun.
C) the photosphere is much less dense than the convection zone.
D) its high luminosity provides plenty of photons, resulting in extreme definition.
E) the Sun has a distinct surface.