Sentence Correction

[/u]According to its propponents, a proposed new style of aircraft could,by skimming along the top of the atmosphere, fly between most points on Earth in under 2 hours.

a)According to its propponents, a proposed new style of aircraft could,by skimming along the top of the atmosphere, fly between most points on Earth in under 2 hours.
b) by skimming along the top of the atmosphere, proponents of a proposed new style of aircraft say it could fly between most points on Earth in under 2 hours
c) a proposed new style of aircraft could fly between most points on earth in under 2 hours, according to its proponents, with it skimming along the top of the atmosphere
d) a proposed new style of aircraft, say its proponents, could fly between most points on earth in under 2 hours because of its skimming along the top of the atmosphere
e) according to its proponents, skimming along the top of the atmosphere makes it possible that a proposed new style of aircraft makes it possible that a proposed new style of aircraft could fly between most points on earth in under 2 hours

please indicate what is the correct answer and why each answer is right/wrong