Agroup of scientist study the effect of chemical on various strains of bacteria. strain a started with 12000 cells and decreases at a constant rate of 4000 cells per hour after the chemical was applied. strain b started with 6000 cells and decreased at a constant rate of 3000 cells per hour after the chemical was applied. when will just strains have the same number of cells? explain

C)He should also take a sample from each of the other history classes in all of the other grades in the middle school.

Step-by-step explanation:

Not only students in the 8th grade are in the middle school, there are other students in other grades who are in the middle school and are enrolled in history classes. Leo's sample is only from one grade of the middle school. In fact, including Ms. Lopez's and Mrs. Frank's classes in the selection of sample is not sufficient. Leo has to take a sample from the remaining grades to avoid making a wrong conclusion as a result of bias in the choice of data.