Here is the sentence:

On Sunday Michael spent the afternoon waxing his new car. If he had knew about the two pop quizzes on Monday, he would have given his algebra problems and accounting spreadsheets more attention.

The second verb, had knew, is incorrect. As you know, this verb requires the past participle known because of the auxiliary verb had.

Know is an irregular verb; the chart below shows its forms.

Verb Simple Present Simple Past Past Participle
know know(s) knew known

Go to the next sentence, champ!

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