1. For each of the following sets, tell whether it is a group or is not a group. If it is a group, provide an explanation. If it is not a group, show which group axiom(s) it does not satisfy. (a) The nonnegative integers under addition (b) The positive rational numbers under multiplication 2. List the elements in (Zi1)2={x2mod11:xZi1} and (Zi3)2={x2mod13:xZ13}