Suppose you want to determine whether there is difference in wait times at two Department of Motor Vehicles offices. A random sample of customer wait times is obtained for each office. Which test(s) can be used for each situation below? 

a. The populaton distribution of wait times is approximately Normal for both groups.

b. The population distribution of wait times for one of the offices is skewed left.

Choose from the following tests, as appropriate: paired t-test, sign test, two-sample t test, and Mann-Whitney test. There may be two acceptable choices.