81
85
6
9 E. None of the above
Answer is Right!
Answer is Wrong!
The correct answer is $\boxed{\text{A}}$.
The impedance ratio of a transformer is the square of the turn ratio. In this case, the turn ratio is 9, so the impedance ratio is $9^2 = 81$.
Option B is incorrect because it is the square of the turn ratio plus 1. Option C is incorrect because it is the square of the turn ratio minus 1. Option D is incorrect because it is the turn ratio itself. Option E is incorrect because it is none of the above.