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
Here parallelism is being tested. A is most parallel --------> propel or help
that -----> refers to jet engine.
Another example :
1. This is one of the cars that
run on hydrogen
that refers to cars
2. Cleveland is one of a large number of communities
on the Great Lakes that
are looking to improve the quality of urban life
that refers to communities NOT to Great Lakes
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