If $p, q, r$ are $+$ ve and are in $A . P$., the roots of quadratic equation $p x^{2}+$ $q x+r=0$ are all real for
(a) $\left|\frac{r}{p}-7\right| \geq 4 \sqrt{3}$
(b) $\left|\frac{p}{r}-7\right| \geq 4 \sqrt{3}$
(c) all $p$ and $r$
(d) no $p$ and $r$