The modulo operator (%) returns the remainder of an integer division. To find the rightmost digit of any integer in a base-10 system, you can find the remainder of that integer when divided by 10. For the integer q = 7777, the expression q % 10 evaluates to 7777 % 10, which results in a remainder of 7, the rightmost digit.

A. 10 % q calculates the remainder of 10 divided by 7777, which is 10, not the rightmost digit of q.

C. q / 10000 performs integer division of 7777 by 10000, which results in 0.

D. q % 10000 calculates the remainder of 7777 divided by 10000, which is 7777.

1. Van Rossum, G. (2023). The Python Language Reference. Python Software Foundation. Section 6.7, "Binary arithmetic operations". The documentation specifies that x % y yields the remainder from the division of x by y.

2. Downey, A. B. (2015). Think Python: How to Think Like a Computer Scientist (2nd ed.). Green Tea Press. Chapter 2, "Variables, expressions and statements," Section 2.6, "Operators and operands." The modulo operator is explained as working on integers to find the remainder.

3. DeNero, J. (2020). Composing Programs. University of California, Berkeley. Section 1.5.2, "Division." "The remainder operator, %, computes the remainder of a division."