Final answer:
The present perfect tense involves the use of 'has' or 'have' with the past participle of the verb. The completed sentences are: 'My brother has cleaned the windows' and 'The girl has had her breakfast.'
Step-by-step explanation:
Understanding the Present Perfect Tense
The present perfect tense is used to describe actions that have been completed at some point in the past but are connected to the present. The structure of the present perfect tense is have/has + the past participle form of the verb.
For the sentences you provided, the correct present perfect tense forms of the verbs in brackets are:
My brother has cleaned the windows.
The girl has had her breakfast.
Remember, we use has for singular third person subjects (he, she, it), and have for all others.