A中"that could eventually propel aircraft anywhere in the world within two or help"做定语修饰a new type of jet engine ；propel和help并列。 定语太长后置。 B中could和have the capability of 重复，propering和to help不对称 c中able to这个形容词短语使用很不恰当 d中改变句子重心（重心是测试）而且propel和helping不并列 e中could和have the capability of 重复，改变句子重心， 当然，987A中within two后面肯定少了一个hours 请指正！
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