well, d has two problems, at least:
- 'projects X to do Y' is unidiomatic. (you can just say 'projects NOUN', as is done in choice e, or you can say something like 'projects that X will do Y').
- an average is a single data point, so there's no such thing as 'averag[ing] from 1.8 to 6.3'. on the other hand, it's quite possible for a single data point to fall between two given values.

i've seen 'of between' in this sense before - think of the phrase 'between 1.8 and 6.3' as standing for a single number, and parse the sentence accordingly (it reads as if it said 'average g.w. of 5 degrees', for instance) - so, if the original poster has copied the problem correctly, we now know that the gmat accepts that construction.