John investigated the properties of two minerals and recorded his observations: Feldspar is a gray, dull, solid that has flat surfaces.
Calcite is a white, dull, solid that has flat surfaces.

What evidence could John use to conclude that both minerals are non-metallic? (2 points)
a
Both minerals are dull.

b
Both minerals are solids.

c
Both minerals have flat surfaces.

d
Feldspar is gray, while calcite is white.