Var (X) = ?

(A) E[X²]
(B) E[X²] – E[X]
(C) E[X²] + E[X]²
(D) E[X²] – E[X]²

The answer is: (D) E[X²] – E[X]²
Explanation
By definition, Var (X) = E[X²] – E[X]²