Though I got this question wrong, I learned new thing.
(A) Degler does more than merely summarizing >> It would have been correct if we compared gerund 'summarizing' with another gerund. For example, Degler does editing more than merely summarizing. In this case 'editing' and 'summarizing' are parallel.
(E) Degler does more than merely summarize >> Though it sounds awkward, grammatically it is correct. here 'does' and 'summarize' are being compared and are parallel.
My mantra for cracking GMAT:
Everyone has inborn talent, however those who complement it with hard work we call them 'talented'.
+1 Kudos = Thank You Dear
Are you saying thank you?