Find the forms of the irregular forms and learn them:
To buy, to choose, to pay, to do, to hear, to know, to misunderstand, to spend, to tell, to see, to rise, to mean, to shake, to send, to become, to fell.

To buy- bought -bought

to choose-chose -chosen

to pay-paid-paid

to do-did- done

to hear- heard- heard

to know- knew- known

to misunderstand- misunderstood - misunderstood

to spend- spent- spent

to tell- told-told

to see-saw-seen

to rise- rose- risen

to mean-meant-meant

to shake-shook-shaken

to send-sent-sent

to become- became-become

to fell-fall- fallen