Sentence Correction

I need help with this question.........

E -- conveys a different meaning.

agree with aj5105

Although would be used if you wanted to say something like:
"Although the ramjet cannot do this.... but it can do that..." In essence you are talking of the ramjet only.

In the question, we are comparing ramjet with scramjet which is another entity hence correct usage is "Whereas one can needs this... the other does not..."

Hope I have made sense.

Now that I look at it, B also compares the right things, ramjets to scramjets.

B expresses paralellism:
can ......can
ramjet .... scamjet
whereas correctly states conflict meaning.