Sentence Correction

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 and 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 exchange 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 wathchdog group recently uncovered a trick that will enable an interloper to rig and E-mail message so that this person was privy to any comments that a recipient might add.
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{A} Tense issue - recipient had added as the message is forwarded

{B} Tense issue - that a recipient might have added

{C} "who still were harboring the illusion" is awkward; "would" is not correct usage here

{E} Tense issue - had been private

[spoiler]{D}?[/spoiler]

The credited response is D .

A detailed explanation is given by gmat pill instructors on gmatclub . here is the link

https://gmatclub.com/forum/gmat-pill-pre ... 52791.html

I thought words such as those and these should be explicitly followed by the noun to avoid ambiguity. At least that's what MGMAT SC says?
So I ended up with C.

D. still harboring the illusion that E-mail exchange 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

I do not agree with D for the following reason : "E-mail exchange ARE"

IMO none of the answer choices seem right . Please help me out