Answer:
D, all the students in each grade
Explanation:
Since the teacher wants to find out the opinion of the the entire school, they should take a random sample from each grade because it is representative of the population they want to sample. If it was just boys, it would exclude the girls, and vice versa for the girls. The teachers aren’t part of the population the teacher wants to survey, so the teacher shouldn’t survey them. Thus, that leaves the random sample from each grade.