The probability that a communication system will have high fidelity is 0.81. The probability that the system will have both high fidelity and high selectivity is 0.18. The probability that a given system with high fidelity will have high selectivity is A. 0.181 B. 0.191 C. 0.222 D. 0.826

The correct answer is $\boxed{\text{B) 0.191}}$.

The probability that a given system with high fidelity will have high selectivity is the probability of both high fidelity and high selectivity, divided by the probability of high fidelity. This is calculated as follows:

$$P(\text{high selectivity}|\text{high fidelity}) = \frac{P(\text{high fidelity and high selectivity})}{P(\text{high fidelity})} = \frac{0.18}{0.81} = 0.191$$

Option A is incorrect because it is the probability of high fidelity and high selectivity, not the probability of high selectivity given high fidelity.

Option C is incorrect because it is the probability of high selectivity, not the probability of high selectivity given high fidelity.

Option D is incorrect because it is the probability of high fidelity, not the probability of high selectivity given high fidelity.