Code Example 4-1 def get_username[first, last s first + + last return s.lowerl def main: first_name input Enter your first name: last name=input("Enter your last name:") username -get username[first_name, last_name printl Your username is:username) main Refer to Code Example 4-1: What arguments are defined by the get usernamel function? username b. , first, last C. first, last d. first name, ast name Code Example 4-3 ma n program: arithmetic as a def main: numi 5 num2 6 resuit -a.add[numi, num2] print The sum is, resuit) if namemain main arithmetic module def addfx 4, y 2): return z Refer to Code Example 4-3: What will be displayed after the code runs? The sum is 11 The sum is 6 The sum is 17 Nothing, the code causes an error b. d