Final answer:
The verb that fills in the blank is comienza. In the present tense, the verb comenzar means 'to start' or 'to begin'.
Step-by-step explanation:
The verb that fills in the blank is comienza. In the present tense, the verb comenzar means 'to start' or 'to begin'. So, the sentence 'La clase comienza a las diez' translates to 'The class starts at ten'.
Learn more about Spanish verb conjugation