Answer
Expression 1 goes with expression F to build an identity.
Work Step by Step
According to the given identity, we have that $$\cos(x+y)=\cos x\cos y-\sin x\sin y$$
Here we cannot do any further simplifications.
Now we match with the expressions in II. We find that the first expression in I matches the expression F in II.
Therefore, we would match 1 with F to have an identity.
