Final answer:
The product labeled to expire 1299 should be used by December 31, 1999. This is understood by interpreting '12' as December and '99' as the year, conventionally ending with the last day of that month if not otherwise specified.
Step-by-step explanation:
When a product is labeled to expire 1299, the label is using a shorthand notation that typically represents the month and year of expiration. In this format, '12' would stand for December, and '99' would indicate the year 1999. Therefore, the product expires in December of 1999. However, the exact last day of the month is not specified in the shorthand '1299'. By convention, if the day is not specified, it is usually understood to be the last day of that month.
Given the options presented, the closest and most logical date would be D. 12/31/99,
which is the last day of December in 1999. It's important to note that option C, 11/31/99, is not a valid date since November only has 30 days.