Thanks. I could not understand usage of comma after 'and'.
B and C are out because of 'they'.
E is out because of 'the cost is'
You cannont make the 'carrying as many as..' bit a modifier. Here it should be part of the main clause because you want to compare that fact with the the number in other vans. Turning it into a modifier renders the information somewhat inessential.
A is best.