Review the item:
Juan herd his mother calling from down the street but chose to ignore her summons. Although he knew that she would be angry about his late arrival for dinner, he had to finish his inspection of the dead toad on the sidewalk.

The first verb, herd, is the problem. The sentence requires the simple past. Heard is the correctly spelled form.

Verb Simple
Present
Simple
Past
Past
Participle
hear hear(s) heard heard

Chose, the verb you chose, is perfectly correct. Before you continue, review the rules for irregular verbs.

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