Final answer:
The completed sentence using the present simple tense of the verbs given is: "Our lessons start at 9.00 and finish at 3.30."
Step-by-step explanation:
The correct present simple forms of the verbs 'start' and 'finish' to complete the sentence are 'start' and 'finish'. Therefore, the completed sentence is: "Our lessons start at 9.00 and finish at 3.30." The present simple is used here because it refers to a regular schedule or routine. Remember that in the present simple tense, the base form of the verb is used for all persons except the third-person singular, which usually ends in -s or -es. Since the subject 'our lessons' is third-person plural, the base forms 'start' and 'finish' are used directly without any additional suffix.