smc

Notice that for any directly or inversely proportional values, it can be expressed as $\frac{x}{y}=k$ or $xy=k$. Now we try to convert each into its standard form counterpart. $\text{(A)}x+y=0⟹\frac{x}{y}=-1$ $\text{(B)}3xy=10⟹xy=\frac{10}{3}$ $\text{(C)}x=5y⟹\frac{x}{y}=5$ $\text{(E)}\frac{x}{y}=\sqrt{3}⟹\frac{x}{y}=\sqrt{3}$ As we can see, the only equation without a "standard" form is $\text{(D)}$, so our answer is $\boxed{3x+y=10}$