Sentence Correction

The National Transportation Safety Board has recommended the use of fail-safe mechanisms on airliner cargo door latches assuring the doors are properly closed before takeoff and to prevent them from popping open in flight.

(A) assuring the doors are properly closed
(B) for the assurance of proper closing
(C) assuring proper closure
(D) to assure closing the doors properly
(E) to assure that the doors are properly closed

[spoiler]A,B,C are clearly out because of faulty parallelism. What is wrong with D?[/spoiler]

The phrase 'closing the doors properly' is impersonal - it does not indicate who or what is the grammatical subject that performs the action of closing. The original sentence is clear about this - the doors are the passive grammatical subjects: 'the doors are properly closed'. Answer choice E preserves the passive construction and hence the meaning of the original sentence.
Because it is phrased impersonally, answer choice D could be misconstrued to mean that the design of the latches assure 'someone's' closing the door, but the latches are part of the door mechanism - they do not assure that the person closing the door will perform a correct action, close it properly but rather that the physical object - the door - will be closed properly (and stay closed).

Thanks Ilana!