Here is the item:
If Tyree had __________ how beautiful the substitute teacher was going to be, he would have prepared his math homework—instead of an arsenal of spitballs—to impress her with his intelligence.

The blank requires the past participle of know, an irregular verb. You chose known, the correct form. Hallelujah!

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

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