Answer
5 is matched with E.
Work Step by Step
According to the given identity, we have that $$\cos(x-\frac{\pi}{2})=\sin x$$
which is a little unlike the fifth expression. So we need do some transformations: $$\cos(\frac{\pi}{2}-x)$$ $$=\cos[-(x-\frac{\pi}{2})]$$
Yet we already know that $\cos(-X)=\cos X$. Therefore, $$=\cos(x-\frac{\pi}{2})$$ $$=\sin x$$
Now we match with the expressions in II. We find that the fifth expression in I matches the expression E in II.
Therefore, we would match 5 with E to have an identity.
