When does Bob's Medicare Part B enrollment begin if his 65th birthday is July 15?

Bob's Medicare Part B enrollment begins three months prior to his 65th birthday month, which is July. This means that his enrollment period starts on April 1. The initial enrollment period for Medicare Part B includes the three months before the month of the person's 65th birthday, the month of the birthday itself, and three months after. Since Bob's birthday is on July 15, his enrollment window stretches from April 1 to October 31. Therefore, the correct answer identifies that enrollment begins at the start of April, aligning with the standard rules governing Medicare enrollment periods.