There is no hard and fast rule regarding this subject. A. rule that is difficult B. rule that is fat changing C. rule that cannot be broken or modified D. rule that can be broken or modified

The correct answer is: D. rule that can be broken or modified.

A hard and fast rule is a rule that is very strict and must be followed without exception. It is a rule that is not open to interpretation or modification.

Option A is incorrect because a hard and fast rule is not necessarily difficult. It may be easy to follow, but it is still a rule that must be followed without exception.

Option B is incorrect because a hard and fast rule is not necessarily fat changing. It may not have any effect on a person’s weight, but it is still a rule that must be followed without exception.

Option C is incorrect because a hard and fast rule is not necessarily a rule that cannot be broken or modified. It may be a rule that is difficult to break or modify,

In conclusion, the correct answer is: D. rule that can be broken or modified.