Please answer question 9 for me to find correct solution.

The CPA firm auditing YU Company found that net income had been overstated. Which of the following errors could be the cause? 9. Failure to record collection of an account receivable balance at the end of the period. Failure to record payment of an account payable on the last day of the year. Failure to make an adjusting entry to record revenue which had been earned but not yet billed to customers. moowi Failure to make an entry to record purchase of land for cash on the last day of the year. None of the above