Final answer:
The correct verb form is 'está' which means 'to be' in Spanish and denotes a temporary state of being tired.
Step-by-step explanation:
The correct verb form to fill in the blank in the sentence is B. está.
The sentence can be translated to English as: The teacher is always tired.
The verb form está is the third-person singular present tense of the verb estar, which means 'to be' in Spanish. In this context, it denotes a temporary state or condition of being tired.
Learn more about Verb forms in Spanish