Sing-sing noticed that whenever she opened the door to the pantry, her dog would come into the kitchen and act hungry, by drooling and whining. She thought that because the dog food was stored in the pantry, the sound of the door had become a(n) .

Donald is studying the eating habits of all students attending his school. he samples the population by dividing the students into groups by grade level and randomly selecting a proportionate number of students from each group. he then collects data from the sample. which type of sampling is used? select the correct answer below: systematic sampling convenience sampling stratified sampling cluster sampling