The equation that has a constant of proportionality equal to \(1\) is:
(Choice D)
\[y=x\]
In this equation, \(y\) is directly proportional to \(x\) with a constant of proportionality of \(1\). In other choices, the constant of proportionality is represented by the coefficients of \(x\) (for example, \(\frac{10}{11}\) and \(\frac{7}{8}\)), which are not equal to \(1\).