1. 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. (A) tested that could eventually propel aircraft anywhere in the world within two or help (B) tested that could eventually have the capability of propelling aircraft anywhere in the world within two hours or to help (C) tested, eventually able to propel aircraft anywhere in the world within two hours, or helping (D) tested, and it eventually could propel aircraft anywhere in the world within two hours, or helping（A） (E) tested, and it could eventually have the capability to propel aircraft anywhere in the world within two hours or help
After more than four decades of research and development这个时间状语的作用范围
有and存在也许只对前面分句a new type of jet engine is being tested；不过更可能是‘After more than four decades of research and development,’修饰整个句子，这样就产生不合理的意思：After more than four decades of research and development, it could eventually have the capability to propel aircraft anywhere in the world within two hours or help。避免这种歧义的产生最好的方法是用;分开。我的疑惑是，这种歧义指的是什么呢？ 谢谢大家！ | 
