What are the rules used to calculate the number of strings of lowercase letters of length four or less, not counting the empty string?
A) The number of strings for each length is calculated using the formula 26n, where n represents the length of the string.
B) The number of strings for each length is calculated using the formula (26n) - 1, where n represents the length of the string.
C) The number of strings for each length is calculated by taking 26 raised to the power of n, where n represents the length of the string, and subtracting 1.
D) The number of strings for each length is calculated by taking 26 raised to the power of n, where n represents the length of the string.
