This question requires applying the principle exactly as it is worded, rather than the more familiar general rule that a wrongdoer cannot profit from his own wrong. Let's test each option against the text given.
Because the principle expressly permits a person to take advantage of his own wrong, and the legatee's wrong is exactly what caused the testator's death, the legatee remains entitled to the benefit under the will.
Therefore, the correct answer is The legatee can take the benefit under the will.
This principle needs to be read exactly as worded, since it states the reverse of the more familiar rule that a wrongdoer cannot profit from his own wrong. The relevant elements are simply, was a wrong committed by the party in question, and does the principle, as stated, permit that party to benefit from it. Checking each option against this literal wording.
Reading the principle exactly as it is worded, rather than substituting the more familiar contrary maxim, permits the legatee to keep the benefit under the will despite causing the testator's death.
Therefore, the correct answer is The legatee can take the benefit under the will.