Solve the following equation. \[ \log _{40} \mathrm{x}=0 \] Select the correct answer below and, if necessary, fill in the answer box to complete your choice. A. The solution set is \{\} (Simplify your answer.) B. The solution set is $\{x \mid x>0, x \neq 1\}$.

Step 1 ：The given equation is \(\log _{40} \mathrm{x}=0\).

Step 2 ：The base of the logarithm is 40 and the argument is x. The equation is equal to 0.

Step 3 ：In general, for any base b, \(\log_b{1} = 0\).

Step 4 ：Therefore, the solution to this equation is when x equals 1.

Step 5 ：So, the final answer is \(\boxed{\{1\}}\).