super easy Combination question

Question

Jessica is taking math, science, and language arts as her 1st 3 classed of the day. In how many orders can sh take the classes.

A. 12

B. 9

C. 6

D. 3

Answer 1

the answer is C, 6:  for the first period, 3 choices; 2nd period, 2; last, or third, period, only one possibility left .. so, 3*2*1 (or 3!, 3 factorial0) is 6.