me question. I point(s) possible ubmit quiz Indicate whether the following study is an observational study or a controlled experiment. A researcher is interested in the effect of music on memory. She randomly divides a group of students into three groups: those who will listen to quiet music, those who will listen to loud music, and those who will not listen to music. After the appropriate music is played (or not played), she gives all the students a memory test. Select the correct answer below. OA. This is a controlled experiment. She assigns students to the control and treatment groups at random in order to control for all relevant factors aside from the effect of music on memory, which is essential to conducting a controlled experiment. OB. This is an observational study. The number of treatment groups is not sufficiently large to control for all relevant factors aside from the effect of music on memory; a large number of treatment groups is essential to conducting a controlled experiment. OC. This is an observational study. The researcher observes only the results of the memory test. Without observing the subjects' performance on memory tests prior to assignment to different groups, the study is not sufficiently active to make this a controlled experiment. OD. This is a controlled experiment. She controls for other factors prior to assigning students to the control group and two treatment groups. This is essential to conducting a controlled experiment.