Determine whether the following is an observational study or an experiment??

(aa)) A MACT 2222 instructor announces a revi ew session to be held the day before a test.. The instructor lists the students who attended the session and compares their scores to the remaining MACT 2222 students ' scores..

(bb)) To assess whether a new teac hing method will improve the students ' understanding , a MACT 2222 instructor splits his /hher class into two groups.. The instructor then ask s one group to attend the class with that has a new teaching method and the other group to attend the class that has t he old teaching method and compares the test results of each group..