Hi,
well this one is not that obvious. I think in the questions like this one we have to find a strong connection between the thesis and the argument which is supposed to weaken or support the thesis. So if the thesis is as follows:
Therefore, such gifts exacerbate rather than lighten the demands made on a museum's financial resources.
the argument we looking for has to refer to the gifts and costs not to the donator or museum etc. The only one fullfilling this criteria is E., this is the only one telling sth about gifts, and the conclusion is: if the museum didn't get the gifts from the donator some of them (objects) are of such importance that the museum would have to buy them by itself and bear the costs of storage anyway.
hope it helps
Joanna