The dark-colored silicate minerals all contain?

Question

a. iron
b. sulfur
c. calcium
d. aluminum

Answer 1

A) iron

Although the question is a bit misleading.
First what does it mean by dark? Black? Dark brown? Dark green? Nevertheless, even if you include most everything you could consider a little dark, the majority contain iron (if only as one end member of a solid solution. That's not true for aluminum and sulfur and while many dark colored silicate minerals contain calcium, many do not. For example:
Anthophyllite - (Mg,Fe)7Si8O22(OH)2 (brown-green)
Biotite - K(Mg,Fe)3(AlSi3O10)(OH)2 (black-brown)

Answer 2

Iron (fe)

I think it is related to Mafic (dark) rocks.
Mafic rocks are generally composed of Magnesium and Iron.
They are generally dark and heavy.

Answer 3

Yup, GatorGal's nailed it, I couldn't have answered better myself. Although I'm the sort of obtuse character that would put down

e. Silicon.