4.20 If $r>0$, then for all $p, q$ such that $p q \neq 0$ and $p r>q r$, we have
(A) $-p>-q$.
(B) $-p>q$.
(C) $1>-\frac{q}{p}$.
(D) $1<\frac{q}{p}$.
(E) None of the above.
(21st American High School Mathematics Examination, 1970)
[Sol] If $pr > qr$, and $r > 0$, then $p > q$, i.e., $-p < -q$. Since $r > 0$, then $\frac{q}{p}q \geqslant 0$, which implies $q > -p$, thus option $(B)$ is incorrect;
and when $p > 0$, $q < p$, we have $-q > p > 0$ or $-\frac{q}{p} > 1$, thus option $(C)$ is incorrect.
In summary, the correct choice is $(E)$.