题目选项分析

After more than four decades of research and development, a new type of jet engine is being tested, and it could eventually have the capability to propel aircraft anywhere in the world within two hours or help boost cargoes into space at significantly lower costs than current methods permit.

After more than four decades of research and development, a new type of jet engine is being tested that could eventually propel aircraft anywhere in the world within two hours or help boost cargoes into space at significantly lower costs than current methods permit.