Define the rule that determines the optimal level of consumption, providing both a verbal description and the corresponding formula. (13 points)
Options:
A. Verbal description and formula for optimal consumption level
B. Explanation and equation for determining the optimal consumption level
C. Describe the rule for finding the optimal consumption level, including both a verbal explanation and the corresponding formula
D. State the verbal description and formula that determines the optimal level of consumption
Note: Unnecessary space and words have been removed.