Final answer:
The writer should keep sentence 11 because it introduces important data regarding the risks of cosmic radiation, reinforcing the argument about the dangers of long-duration spaceflight.
Step-by-step explanation:
The writer should keep sentence 11, as it introduces new data that complements the writer's argument about the health risks associated with long-duration spaceflight. This sentence specifically addresses the risk of cosmic radiation, which is an important factor in discussing the broader implications of space travel on human health. It relates to the overall concern of the paragraph by identifying one of the serious physical challenges that need to be overcome before humans can safely engage in prolonged space missions, thereby supporting the writer's line of reasoning.
The writer should keep sentence 11, which states that cosmic rays pose a health concern and can lead to stomach and colon cancers. This supports the claim made in sentence 10 about the potential for dangerous diseases caused by cosmic radiation. The sentence provides data to support the claim made in the third paragraph.