1) Backstroked 2) Crawled 3) Did laps 4) Dog-paddled 5) Done laps 6) Done laps in a pool 7) Done laps in the pool 8) Done some strokes 9) Done the backstroke 10) Done the crawl 11) Enjoyed the water 12) Floated in water 13) Gone across a pool 14) Had done laps in water 15) Had taken the plunge 16) Has done some laps 
• (p. p.) of Swim • of Swim • imp. & p. p. of Swim.
Swum imperfect & past participle of Swim .