Police chief: This department's officers are, of course, prohibited from drinking on the job.
Given that ...
Cops are usually prohibited from drinking on the job.
Why is it that ...
Cops are allowed to drink in moderation during work if they're working undercover in nightclubs?
Evaluate / Goal
This one seems to play off common sense, so we can probably predict the answer.
Why are cops allowed to drink if they're working undercover in a nightclub? Because they're supposed to be blending in with all the normal people there, most of whom are drinking.
Let's look for that, or any other reason why cops working undercover in a nightclub are allowed to have a couple drinks.