Degler does more than merely summarizing existing research

Option A: This statement is a direct speech of what's reported in the writer's statement which is obviously a Reported speech. It renders the statement weak and uninformative. This option is wrong.

Option B: Here, it's linguistically obsolete to end a sentence with a preposition i.e. 'of' except it's a collation in which case not related ton the main clause. Hence, this is wrong.

Option C : This shows a pre-existing action with a view to furthering it. has being an auxiliary verb helps to decide the time of action with done which invariably doesn't conform to the continuity sense of Does in the writer's specification. This option is wrong.

Option D: merely here suggests it's an adverb whose job is to modify a verb. Summarize is a verb which should come after the word 'merely' to give it a sense of a complete sentence and not the other way round. This option is wrong.

Option E: A statement that shows a strong lexical orientation. The adverb 'merely' here, comes before the Action word which is 'summarize' which suits the arrangement more than the infected form 'summarizing'. This option is correct.