题目选项分析

Whereas a ramjet generally cannot achieve high speeds without the initial assistance of a rocket, scramjets, or supersonic combustion ramjets, can attain high speeds by reducing airflow compression at the entrance of the engine and letting air pass through at supersonic speeds.

Whereas a ramjet generally cannot achieve high speeds without the initial assistance of a rocket, that high speeds can be attained by scramjets, or supersonic combustion ramjets, is a result of their reducing airflow compression at the entrance of the engine and letting air pass through at supersonic speeds.