GMAT Sentence Correction (SC) | Re: The board recommended that additional funding

B) that additional funding for the town pool’scompletion, which could be open as early as next year, be obtained through private donations not through taxrevenue.
Wrong. Modifier error.

D) that additional funding for the completion of the town pool, which could be open as early as next year,be obtained through private donations not taxrevenue.
Correct. Subjunctive mood. Note: the second preposition "through"[through tax revenue] can be omitted.

Hope it helps.