storage space is not actually required.
MBAMantra, on the contrary, exhibit space may be more expensive than storage space. Besides, there is no suggestion that routine conservation is required only for stored artifacts rather than all artifacts.
Therefore IMHO, A would not qualify for an answer.
Now look at E.
(E) Objects donated by a patron to a museum are often of such importance that the museum would be obliged to add them to its collection through purchase if necessary.
This means that museum can usually get things from patrons that otherwise it would have purchased from outside. Of course this is a significant help to the museum's financial resources.
This most significantly weakens the argument that gifts are a drain on a museum's financial resources.
Who says elephants can't dance?