天山20。NO6

6.                 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

我怎么没办法理解A里THAT的那个重句啊

哪位大哥帮帮忙吧