Answer:
D. After filling all of the sample containers, the students returned to their classroom and placed several microscopes on lab desks.
Step-by-step explanation:
Option A shifts voice.
Option B implies the sample containers return to their classroom and place microscopes.
Option C does not mention that the students were the ones who placed the microscopes.
Option D does not shift voice and correctly states that the students fill the sample containers, return to their classroom, and place the microscopes.
Option D is correct.