Answer
a. False
b. True
c. False
Work Step by Step
$P(x)=x^3+x$,
$P(x)=x(x^2+1)=0$
$x=0$ or $x^2+1=0 x=\pm \sqrt {-1}, x=\pm i$.
Thus,
a. False, the polynomial has only one real zero.
b. True, $0$ is the only real zero of the polynomial.
c. False, $P(x)=x(x^2+1)$ can be factored into linear factors and irreducible quadratic factors, not only linear factors.