Here is the item:
While Clive stood on top of the fire ant mound, several of the insects crawled over his shoes and __________ him on the ankles, sending the poor boy dancing around the yard while slapping at his legs.

The blank requires the simple past of sting, an irregular verb. You chose stung, the correct form. Hallelujah!

Verb Simple
Present
Simple
Past
Past
Participle
sting sting(s) stung stung

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