"Begun" is the past participle of "begin."
Past is : Beat (itself) Past Particle : Beaten
The simple past and past participle is had.
The past participle for shrink is shrunk.shrink / shrank / shrunk
"Encouraged" is the simple past and past participle of the verb "encourage".
The past participle of do is 'done'.
Neutron particle is needed to begin nuclear chain reaction.
The past participle is burst.
The past participle is drawn.
Been
The past participle (and simple past) is loved.
The past tense of begin is began.The future tense of begin is will begin.
infinitive: be past: was/were past participle: been