(A) destroys Hypotheses 1 and 2. Both of these hypotheses hinge on a period of heavy bombardment through the inner solar system that intensified four billion years ago. If new evidence showed that Mars did not experience an increase in the intensity of projectiles between three billion to five billion years ago, then we know that there actually wasn’t a period of heavy bombardment through the inner solar system four billion years ago, thus eliminating Hypothesis 1 and 2 and leaving Hypothesis 3 as our only option.

Additionally, (A) tells us that there was not a period of heavy bombardment on Mars four billion years ago, meaning that the Mars rock discovered on Earth would have been a rare discovery of a coincidence, instead of evidence of a larger trend.

Even Hypotheses 1 and 2 allow for debris from the Moon to reach the Earth––these hypotheses just say that the LHB extended beyond the Earth-Moon system. We already know that the Moon was bombarded; (B) does not support the claim that the bombardment was limited to Earth and the Moon.

It’s generally accepted that the bombardment would have affected the Earth, too. Even Hypotheses 1 and 2 agree that the Earth and the Moon were impacted by the LHB ––these hypotheses just say that the LHB extended beyond the Earth-Moon system. (C) does not support the claim that the bombardment was limited to Earth and the Moon.

(D) weakens the author’s elimination of Hypothesis 3. However, this just puts Hypothesis 3 on a level playing field with Hypotheses 1 and 2. Additionally, (D) only addresses one tiny piece of evidence. Even if this particular rock came from the Moon, it would just take one more tiny rock from Mars to call Hypothesis 3 into question again.

Compare this with (A), which strengthens Hypothesis 3 and destroys Hypotheses 1 and 2.

It’s Hypothesis 2 that claims that the LHB concluded billions of years of heavy bombardment. (E) strengthens Hypothesis 2, not Hypothesis 3.