Which of the Following Is Not True for a Random $a \leq x \leq b$

Multiple Choice

Which of the following is not true for a random variable X that is uniformly distributed over the interval $a \leq x \leq b$ ?

A) E(X) = (a + b) /2.
B) V(X) = $( b - a ) ^ { 2 }$ /12.
C) $\sigma$ = (b - a) /6.
D) $f ( x ) = 1 / ( b - a )$ if a ? x ? b.