Difference between "acrid" and "acidulous"

[Zishuli]

This is a question in TEST # GRE/W97:

5. adj. harsh or corrosive in tone; bitter; blistering; caustic; virulent

(a) sensual
(b) porous
(c) acidulous
(d) acrid

The given answer is (d) " acrid", of course it's undoubtedly correct. I wonder whether the option (c) "acidulous" can possibly be another acceptable answer.

[Gray]

"An acidulous tone had crept into both sides of the conversation, her side with balsamic asseverations and cloying evasions, his with a bite of horseradish astride a malt vinegar redolent of London fogs, fish and chips, and tabloid treacle and gossip (it was, in fact, revolting)."

It seems acidulous is not that harsh.
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