Final answer:
Above-normal gas pressure means there is a surplus of primary air, leading to high carbon dioxide and low oxygen content, which aligns with choice C.
Step-by-step explanation:
Having an above-than-normal gas pressure indicates that there is a surplus of primary air.
This would result in a high carbon dioxide content due to excessive combustion or respiratory activity, and a low oxygen content, as more oxygen is being used in the process.
Hence, the correct answer to the question would be: Having an above-than-normal gas pressure means we have a surplus of primary air, a high carbon dioxide content, and a low oxygen content, which corresponds with choice C.
Surplus, Carbon Dioxide, Oxygen.