Final answer:
The correct usage of the Python input() function is shown in option c where it is written in lowercase and includes a prompt in double quotes.
Step-by-step explanation:
The proper use of the Python input() function is to prompt the user to enter some information and then capture that input as a variable. Among the options provided, the correct one is c. answer = input("enter your answer: "). This code uses the input function correctly by including a prompt string argument in double quotes and assigns the user's input to the variable answer. It is case-sensitive and should be spelled correctly in lowercase. Options a, b, and d either lack the necessary quotation marks around the prompt or use an incorrect case, as Python is case-sensitive with its functions.