A. We don't know how long Mayor Delmont has been in office (we know he is still in office). It seems to support the argument, but mentioning 'earlier in Mayor Delmont's tenure' casts doubts on the assertions of the advertisement. What if those jobs created at that time had a really low pay?
B. It may be a reason why it was easy to increase the average pay, but it doesn't support the argument too strongly.
C. Doesn't support the argument at all.
D. It seems to support the argument of the advertisement. If the jobs eliminated had an average pay, and meantime the new created jobs have higher than average pay, then the average paycheck in the city has been getting bigger. This new information is consistent with the argument.
E. Compares two different subjects.
Between the options, D is the one that most strengthens the argument in the advertisement.