Which of the following is not a combination?

the number of ways a president and vice president can be chosen from a group of 10 people.
the number of 2 person subcommittees that can be chosen from a 10 person committee.
the number of 2 person teams that can be picked form 10 people.

Ahypothesis is: a the average squared deviations about the mean of a distribution of values b) an empirically testable statement that is an unproven supposition developed in order to explain phenomena a statement that asserts the status quo; that is, any change from what has been c) thought to be true is due to random sampling order da statement that is the opposite of the null hypothesis e) the error made by rejecting the null hypothesis when it is true