The discovery of glass being expandable and able to be shaped by human breath revolutionized glassworking to such an extent that today "glassblowing" has become the generic term for all glassworking, whether the glass is blown or formed by other techniques.

(A) of glass being expandable and able to be Parallelism - 'being expandable' not parallel to 'able to be shaped'
(B) of glass that is capable of expansion and Parallelism again - 'capable of expansion' not parallel to 'be able to be shapped' active vs passive voice.
(C) of glass being capable of expansion and that it can be Same again
(D) that glass can be expanded and it is able to be Wordy i think
(E) that glass can be expanded and Most direct and clean choice

[spoiler]OA: E[/spoiler]

I also think that 'discovery 'that is better usage than 'discovery of' in this case, but don't think its a GMAT rule.
Hope this helps.

Eliminate A and C because of 'being'
B changes the meaning of the sentence. It says that 'discovery is capable of'
D Wordy and 'it' doesn't has clear reference.
E is correct.
Let us know if u have any specific question.

1. "able to" is the Idiom, not "able to be", so A, D out
2. In B, and C, expansion is paralleled to Shaped, wrong.
3. E takes care of 1 and 2; Expanded and Shaped. So E.