Final answer:
Mock five partnership must use the August 31 year-end because Pops, Inc. has the latest year-end among the three partners.
Step-by-step explanation:
The year-end that mock five partnership must use is determined by the partner with the latest year-end. In this case, Pops, Inc. has an August 31 year-end, which is the latest among the three partners. Therefore, mock five partnership must use the August 31 year-end.