If we want to STRENGTHEN an argument, we must first determine how the argument is currently logically flawed, i.e. what information it's missing.

Premises:
The routine use of antibiotics can give rise to resistant bacteria capable of surviving antibiotic environments

Explanation 1:
The presence of resistant bacteria in people could be due to the human use of prescription antibiotics

Scientists' alternative explanation:
Some scientists, however, believe that most resistant bacteria in people derive from human consumption of bacterially infected meat

Logical Gap:
- do we know that meat is infected?
- are the people who get infected eating this infected meat?
- do humans who do *not* take antibiotics sometimes get these infections?

In order to strengthen the argument, we want to make Explanation 1 less likely, and Explanation 2 more likely.

(A) Antibiotics are routinely included in livestock feed so that livestock producers can increase the rate of growth of their animals.
This increases the odds that a lot of meat is infected with antibiotic-resistant bacteria.

(B) Most people who develop food poisoning from bacterially infected meat are treated with prescription antibiotics.
This could still be a very small portion of people, and others could be getting the infection *not* from meat. We need to support the idea that a large proportion of infections come from meat. This doesn't speak to frequency of meat-related infections.

(C) The incidence of resistant bacteria in people has tended to be much higher in urban areas than in rural areas where meat is of comparable quality.
This would actually weaken the idea that the contamination is from meat. If a lot of meat is contaminated, it should affect people equally in different areas (assuming that "comparable quality" implies "comparable rates of infection").

(D) People who have never taken prescription antibiotics are those least likely to develop resistant bacteria.
This would support explanation #1, not #2.

(E) Livestock producers claim that resistant bacteria in animals cannot be transmitted to people through infected meat.
This undermines the scientists' claim, not supports it.

The answer is A.