Final answer:
The valid Python code comment is 'a. # use comments to describe the function of code', as comments in Python are indicated with a '#'. Other options do not reflect the correct syntax for comments in Python.
Step-by-step explanation:
The valid Python code comment from the provided options is a. # use comments to describe the function of code. In Python, comments are indicated by the # symbol at the beginning of the comment text. Everything following the # on that line is treated as a comment and is not executed as part of the program. Option b is incorrect because in Python, comments do not start with a /. Option c is a true statement about comments, but not a syntactically valid comment. Option d is also incorrect because single quotes are not used for comments in Python. Comments are crucial for explaining the code, making it more readable, and providing instructions to other developers or yourself for future reference.