Dr. A. conducts a study on the effect of distraction on learning. Dr. A goes to a local mall and asks shoppers to participate in her study. Those who agree to participate are then randomly assigned to one of three groups. The first group is placed in a quiet room; the second group is placed in a room with a moderate level of background noise; the third group is placed in a room with a high level of background noise. All participants are then given a learning task to complete. The type of sampling strategy used by Dr. A is best characterized as: a. Random b. Stratified c. Convenience d. Snowball Solution a. Random.