Need help with math question

Which of the following problems must be determined using a combination? 0 Determine the number of ways Billy and Samantha can be chosen when a group of 5 is selected from a class of 20 students. 0 Determine the probability of rolling doubles with a pair of dice. 0 Determine how many ways 10 people can sit on a bench. O Determine the number of ways a President and Vice-President can be chosen from a class of 20 students