Answer:
def main(): will properly start the main() function in Python.
Step-by-step explanation:
def Main will not properly start the main() function because it has a capital M and its missing parentheses as well as a colon.
def main# will not properly start the main() function because it has a unnecessary hash at the end and its missing a colon.
def main[] will not properly start the main() function because it has a unnecessary square brackets at the end and its missing a colon.
so only def main(): will properly start the main() function in Python because it has a correct syntax.