Please find my below reasoning
A. The savings achieved by making drug users ineligible to receive welfare benefits will be greater than the expense of testing all welfare benefit recipients for drug use.- Correct. On negating this option makes the argument conclusion falls apart.
B. People who use illicit drugs and who know that they are going to be tested for drug use can take measures that result in their testing negative for drug use.- Irrelevant. Our conclusion is that taxpayer money must be saved
C. Everyone who engages in the use of illicit drugs becomes dysfunctional and unemployable.- So what? will this lead to save Tax payers money? No..
D. Most people who become ineligible for welfare benefits because of their testing positive for use of illicit drugs will discontinue their drug use and find employment.- Irrelevant. Conclusion does not bother whether they start working or not
E. The percentage of people receiving welfare benefits who use illicit drugs is greater than the percentage of people not receiving such benefits who use illicit drugs.- Again Irrelevant.
Although When i read option A , I was not able to gather the data so I kept that option hold and start reading other options and eliminated them. In the end left with Option A.
Hence Option A is correct