My take here is A:
A)An unrelated survey of annual charitable giving finds that residents of rural areas give 3% less to charity than residents of urban areas.This supports the conclusion, which states that urban dwellers are more generous. Even if in this particular case urban dwellers donated more, this additional info supports the hypotesis that urban residents are in fact more generous.
B)There are more homeless people in urban areas than rural areas, making it more likely that urban residents would contribute to those charities.Since the program in the passage is about homeless people, urban residents are more likely to donate to that cause. But we cannot generalize saying that they are more generous in general. This weakens the conclusion.
C)There are more charities in general operating in urban areas than in rural areas.This could translate in more opportunities to donate, and in this case urban dwellers could donate more not because they are generous, but because they have more possibilities to do so.
I saw a lot of Cs before my post, and here is why I think is not correct:
I go out every day with 5$, willing to donate them. If I live in the city, I can find more charities and I can donate them easily; but if I live in a rural area I cannot (take the case in which there is only one charity organization). Does this mean that I am less generous if I live in the rural area? I don't think so...
This is why IMO C casts doubts on the conclusion.
D)The survey is calculated based on dollar amount rather than percentage of income, and does not account for the fact that incomes in urban areas are often higher.The first part (before the comma) points out that the dollar amount is not a good estimator of the generosity compared to a percentage indicator.
The second part gives credit to the fact that, because incomes in the urban area are higher, the "15 $ difference" should not transalate into more generosity.
E)The group Live in the City has been known to alter survey results for marketing purposes.Since the group is an "urban-promotion group" it could alter the results in favor of the city.