IMO the answer is B. Even though it sounds out of scope, it does provide a solid reason to prove the conclusion of the argument incorrect given the carelessness of workers.
What is the OA? People should post OA answers with their questions. Else it becomes confusing and no one knows what the right answer is. Please be responsible and post the OA.

The correct answer is definitely choice C, as many have pointed out.

Choice C tells us that current workers may actually have a (current) drinking problem. So, by replacing them with those who have been treated for their drinking problem, we may actually decrease the risk of accidents, thereby weakening the argument.

That some companies' policy is to put drinkers in residential treatment is clealy irrelelvant. Thus, choice A is incorrect.

Because the argument was about reducing the risk of accident through a certain policy, that some accidents are attributable to an alternative explanation is irrelevant. Thus, choice B is incorrect.

We don't care that safety-sensiive job holders are more likely to become drinkers. We care about whether the policy against hiring them will lead to a reduction in the risk of accident. Thus, choice D is incorrect.

Choice E is wrong for the same reason that choice B is wrong: that some accidents are attributable to an alternative explanation is irrelevant.

Testluv wrote:The correct answer is definitely choice C, as many have pointed out.

Choice C tells us that current workers may actually have a (current) drinking problem. So, by replacing them with those who have been treated for their drinking problem, we may actually decrease the risk of accidents, thereby weakening the argument.

As you reason above, choice C is strengthened isn't it?

Can you elaborate more for me, please? Thanks

P/S: Let's I try to reason in choice C.

Choice C said that the worker who has now drinking problem did not seek any treatment (for drinking problem) to work as long as possible => bosses cannot reduce the risk of accidents because they cannot find those who have drinking problems. Therefore, this policy is ineffective. Weaken conclusion.

Am I correct?

I think the argument is talking about the relationship:
drinking ~ accident (in the condition: safety-sensitive job)
Therefore, we only care about the above relationship, NOT about the relationship between "safety-sensitive job" and drinking, as Choice (D) said.
In other words, Choice (D) has the element of drinking but not the element of "accident", and thus is out-of-scope.

Also, I think it would be helpful to do mental "role play" in attacking a real-world CR problem.
There's the policy in place, and suppose you are unfortunately someone with this drinking problem and you want to find a job, what would you do? (As Dana said)