GMAT Sentence Correction (SC) | The Diary of Anne Frank tells the true story of a young girl

When two verbs are added, only a conjunction (without a comma) is required.

I read and write.... correct
I read, and write....wrong

When two clauses are added, comma + conjunction is required.

I read, and I write.... correct
I read and I write...wrong

Here notice that two verbs ("were hidden" and " were") are joined by a conjunction ("but")
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