Final answer:
The question asks for a rule regarding the sum of clock digits. None of the provided options are correct, but an accurate pattern is that the hour and minute digits must add up to 6, seen in times like 1:50 and 2:40.
Step-by-step explanation:
The question asked pertains to a rule that determines when the digits on a twelve-hour clock add up to 6. Among the given options, none of them directly answers the question. However, a refined rule that correctly specifies when the sum of clock digits equals 6 could be:
The sum of the digits in the hour and minute must equal 6, including cases where either the hour or minute is composed of two digits.
For example, at 1:50 ('1' + '5' + '0' = 6) or 2:40 ('2' + '4' + '0' = 6), the digits add up to 6. This pattern occurs multiple times throughout a twelve-hour period. A counter-example to the options provided is 1:32 ('1' + '3' + '2' = 6), clearly showing that the sum of digits is not always divisible by 3, the product of the digits is not 6, the sum of the digits is not always a prime number, and the difference between the digits is not always even.