- to a completed action and an indefinite/unspecified time in the pas
- to an action that began in the past and continued to the present time
Here
in the question, we see that the speaker is expressing that David has done his homework and thus can go to bed. Thus the speaker is referring to an action that is completed at the time of speaking (i.e. completion of homework) but no reference to time has been made. Therefore the correct tense to use here is Present Perfect.
Formulation of sentences of Present Perfect Tense: have/has + past participle form of the verb.
"have" is used with : I / you / we / they
"has" is used with : he / she / it
Here the verb is finish, & past participle of finish is -- finished.
Therefore to construct this sentence in Present Perfect Tense we will add "has" + "finished".
Thus,
the correct complete sentence is:
David can go to bed now. He HAS FINISHED his homework.
- Finish is the stem word
- Finishes is 3rd person present
- Finished is past tense