Understanding the argument -
More than a year ago, the city announced that police would crack down on illegally parked cars and that resources would be diverted from writing speeding tickets to ticketing illegally parked cars. Fact
But no crackdown has taken place. "But" introduces a contrast. Fact.
The police chief claims that resources have had to be diverted from writing speeding tickets to combating the city’s staggering drug problem. Claim/Premise
Yet the police are still writing as many speeding tickets as ever. - "yet" introduces a contrast from the previous statement.
Therefore, the excuse about resources being tied up in fighting drug-related crime simply is not true. - Conclusion. Aligned with the contrast and against what the Police chief claimed.
Option Elimination. - we need to find the minimum condition or the missing premise or the assumption for the conclusion to hold: the excuse about resources being tied up in fighting drug-related crime is not true. What if the police could deploy cameras/technology or new strategies and write as many or even more tickets while deploying resources to solve drug-related issues? The basic assumption of the author is that the police can't do both at the same time, and this is what option E highlights.
(A) every member of the police force is qualified to work on combating the city’s drug problem - "qualification" is out of the scope of the argument, which is to find the missing premise for the conclusion to hold: the excuse about resources being tied up in fighting drug-related crime is not true.
(B) drug-related crime is not as serious a problem for the city as the police chief claims it is - judging the police chief's claim is out of scope.
(C) writing speeding tickets should be as important a priority for the city as combating drug-related crime - We are looking for an assumption. Right? What is an assumption? A missing premise or fact? What is this statement? "should be"? Is it an opinion? Can this be an assumption? No. Moreover, at best, from the argument, it seems that drug-related crime is a priority, and this option is trying to establish equal importance for speeding tickets as well, which is out of scope.
(D) the police could be cracking down on illegally parked cars and combating the drug problem without having to reduce writing speeding tickets - First, the "illegally parked cars" are not part of the conclusion and scope of our argument here. Secondly, even if we take the drugs part, it says that police can do both, which directly weakens the conclusion. The assumption, when negated, weakens the conclusion, but not without negating. All assumptions are strengths (while all strengthened can't be assumptions as assumptions that "must be true" or a necessary condition). Opposite of what we need.
(E) the police cannot continue writing as many speeding tickets as ever while diverting resources to combating drug-related crime - ok. When we negate it, the negated option will shatter the conclusion.