You are using the Mann-Whitney U test for a large sample and have been given the following statistics: T = 258, n1 = 15 and n2 = 25. Using a 5 per cent significance level you would compare a z value of:
a. +1.87 with +1.645 and reject null hypothesis
b. +1.87 with +1.96 and not reject null hypothesis
c. -2.87 with +1.96 and reject null hypothesis
d. +2.87 with +1.96 and not reject null hypothesis