Concept:The correct past tense form of the verb "swim" is needed to complete the sentence.
Explanation:The phrase "after school" shows the action is finished in the past.
So the sentence must use the simple past tense.
The simple past form of "swim" is "swam".
"Swum" always needs a helping verb like "has" or "had".
"Swimming" always needs a helping verb like "was" or "were".
"Swim" is the base form, used for the present or future, not for this past action.
Thus, the correct word is "swam".
Answer:A. swam