Consider the following code segment:

import os
filename = input("Enter the name of a file: ")
if ____________________ :
print("That file exists!")
else:
print("That file does not exist.") This code segment is supposed to print an appropriate message indicating whether or not the file specified by the user exists.

What code should be placed in the blank so that the code segment performs its intended task?

a. filename != ""
b. os.path.exists()
c. os.path.exists() == filename
d. os.path.exists(filename)