Final answer:
The best way to correct the verb tense in the sentence is to change 'placing' to 'placed'.
Step-by-step explanation:
The best way to correct the verb tense in the sentence 'Eli placing the brownies in the oven and then he waited' is to change 'placing' to 'placed'. This change makes the verb tense consistent throughout the sentence because both verbs are in the past tense. Changing 'brownies' to 'brownie' or 'Eli' to 'He' would not correct the verb tense error in the sentence. Similarly, changing 'waited' to 'waits' would create a tense inconsistency.