GMAT Sentence Correction (SC) | Literacy opened up entire realms of verifiable knowledge to ordinary

hey

after eliminating all choices only B was left hence i chose B

But i have read in manhattan SC book that had is not used if sentence contains some other term referring back to that time or helping in deciding the sequence of events such asbefore

here also i thinkpreviously establishes that point and hence there should bewere instead of had

please correct me where i am going wrong.

thanks
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