Explanation: The pulse repetition interval (PRI) is the time duration between the start of one pulse and the start of the next pulse in a pulsed system, such as radar or some digital communication systems. The pulse repetition frequency (PRF) is the number of pulses transmitted per second. These two parameters are inversely related. To find the PRI, you simply take the reciprocal of the PRF: PRI = 1 / PRF Given PRF = 2000 Hz: PRI = 1 / 2000 seconds PRI = 0.0005 seconds Therefore, the correct answer is 0.0005 seconds. The other options result from incorrect calculations of this inverse relationship. For example, 0.005 seconds would correspond to a PRF of 200 Hz, and 0.05 seconds would correspond to a PRF of 20 Hz.