Final answer:
The sentence should be: Ellos son profesores y muy inteligentes.
Step-by-step explanation:
The correct form of the verb 'ser' should be used in this sentence because we are describing a characteristic of the professors, which is their intelligence. The correct form is 'son' which means 'are' in English. Therefore, the sentence should be: Ellos son profesores y muy inteligentes.
Learn more about Spanish verb conjugation