Assertion. Python's built-in functions, which are part of the standard Python library, can directly be used without specifying their module name.

Reason. Python's standard library's built-in functions are made available by default in the namespace of a program.

(a)

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Explanation
Python's built-in functions such as print(), len(), range() etc, are automatically added to the program's namespace from the Python's standard library. They can be used directly without importing any modules or specifying their module name.