The equations $\large\frac{x}{a}+\large\frac{y}{b}=$$1$ and $\large\frac{x}{b}+\large\frac{y}{a}=$$1$ are inconsistent if

Question

$( A ) ab=0 \\ ( B ) a+b = 0\\ ( C ) \large\frac{a}{b}=0 \\\ ( D ) a-b=0$