GWD 11-33, key is E,but i use: capability to do ?

Q33:

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 hours 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

tested, and it could eventually have the capability to propel aircraft anywhere in the world within two hours or help

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what is the difference of following two use?

the capability of

the ability to do ...