Geologists believe that one of the largest volcanic eruptions in human

Geologists believe that one of the largest volcanic eruptions in human history occurred 74,000 years ago, the Toba supereruption. In one area, Middle Paleolithic tools of similar styles have been found and dated to closely before and after the Toba supereruption, indicating that the humans who lived after the supereruption were members of the population that had lived in that area prior to the eruption.

Which of the following, if true, most seriously weakens the argument?
A) Most tools used by the population prior to the supereruption were destroyed in the aftermath of the eruption. Irrelevant, because some tools survived the eruption
B) Other evidence indicates that tools of similar styles had been used in the area long prior to the supereruption. Irrelevant. If we know that the local people lived there long before the erruption it doesn't help us to assess whether those people still lived there after the erruption.
C) Some populations under the massive supereruption traveled long distances to attempt to find a better place to live. Irrelevant. This could actually be a strengthener because it could indicate that some other population travelled a lot caused by the erruption and settled at the particular place described in the passage.
D) After the supereruption, a new population might have found and adopted use of the tools that had originally belonged to a population that was destroyed by the supereruption. Correct. If the people inhabitating the region after the erruption used the same tools as the original population, the argument is weakened. Now the resemblance of the tools prior to and after the erruption can't be used to argue for the "same-population-argument" anymore.
E) Research has suggested that many animal species went extinct as a consequence of the supereruption. Irrelevant as animals don't have anything to do with the tools or the population in this particular case.

Hope that helps