In a blow to those who still harbored the illusion that E-mail exchanges are private, a watchdog group recently uncovered a trick for enabling an interloper to rig an E-mail message so that this person will be privy to any comments that a recipient had added as the message is forwarded to others or sent back and forth.

(A) who still harbored the illusion that E-mail exchanges are private, a watchdog group recently uncovered a trick for enabling an interloper to rig an E-mail message so that this person will be privy to any comments that a recipient had added
(B) who had still been harboring the illusion that E-mail exchanges are private, a watchdog group recently uncovered a trick for enabling an interloper to rig an E-mail message so that this person was privy to any comments that a recipient might have added
(C) who still were harboring the illusion that E-mail exchanges are private, a watchdog group recently uncovered a trick enabling an interloper to rig an E-mail message so that this person is privy to any comments that a recipient would add
(D) still harboring the illusion that E-mail exchanges are private, a watchdog group recently uncovered a trick that enables an interloper to rig an E-mail message so that this person will be privy to any comments that a recipient might add
(E) still harboring the illusion that E-mail exchanges had been private, a watchdog group recently uncovered a trick that will enable an interloper to rig an E-mail message so that this person was privy to any comments that a recipient might add
OA is D.
could you help me choose the answer?

what is the difference between C and D? Thanks

a few things about choice c:
(1) 'who were still harboring' is wordy, esp. in comparison to the more concise version 'still harboring' presented in choice d**
(2) 'is privy' doesn't make as much sense as will be privy', because the comments to which the person will be privy haven't been posted yet (it's a future occurrence)
(3) 'would add' can be interpreted in two ways: either as a subjunctive (for a hypothetical that isn't actually true, as in 'i wish you dressed more nicely') or as the past-tense version of 'will'. the first doesn't make sense, because this hypothetical could clearly be true, and the second doesn't make sense because the hack is being described in the present tense, not the past tense. 'might', a present tense construction, makes more sense.

choice d, on the other hand, uses the more concise form 'still harboring' and the correct-tense forms 'will be' and 'might'.