How Many Real Roots Does the Equation $x ^ { 5 } - 7 x + c = 0$

Multiple Choice

How many real roots does the equation $x ^ { 5 } - 7 x + c = 0$ have in the interval $[ - 1,1 ]$ ?

A) at most five real roots
B) no real roots
C) at most one real root
D) at most two real roots
E) at most three real roots