Step 1: Recall the meaning of the Taylor Rule.
The Taylor Rule is a monetary policy guideline proposed by economist John Taylor. It helps Central Banks determine the appropriate nominal interest rate in response to economic conditions.
Step 2: Identify the key variables in the Taylor Rule.
The Taylor Rule mainly depends on:
Inflation gap
which is the difference between actual inflation and target inflation, and
Output gap
which is the difference between actual output and potential output.
Step 3: Write the standard Taylor Rule form.
A simplified Taylor Rule is
\[
i=r^*+\pi+a(\pi-\pi^*)+b(y-y^*)
\]
where
\[
i=\text{nominal interest rate}
\]
\[
\pi=\text{actual inflation}
\]
\[
\pi^*=\text{target inflation}
\]
\[
y-y^*=\text{output gap}
\]
Step 4: Analyze the options.
(A) Incorrect, because the Taylor Rule is not primarily used for setting exchange rates.
(B) Correct, because it determines the nominal interest rate using inflation gap and output gap.
(C) Incorrect, because exchange rate is not a standard component of the Taylor Rule.
(D) Incorrect, because the Taylor Rule is a policy rule for interest rates, not mainly a forecasting tool.
Step 5: Final conclusion.
Therefore, the Taylor Rule is mainly used
\[
\boxed{\text{to set nominal interest rate based on inflation gap and output gap}}
\]
Hence, the correct option is (B).