Final answer:
The correct verb form to fill in the blank in the sentence is 'está'.
Step-by-step explanation:
The correct verb form to fill in the blank in the sentence is está.
In this sentence, the subject is la profesora (the teacher) and the verb form that agrees with this subject is está (is).
For example, a complete sentence using the correct verb form would be: La profesora está cansada (The teacher is tired).
Learn more about Verb forms in Spanish