Pupils from Jefferson High School embarked on a field trip to a neighborhood pond. Thankfully, the weather was clear, enabling the students to accomplish their assigned task. Under the supervision of their instructor, they collected numerous water samples. The samples were safely accumulated by using containers with prolonged handles. After filling all of the sample containers, the students returned to their classroom where several microscopes were placed on lab desks by the students. Then the students anxiously waited in line for an opportunity to peer through one of the devices. While glancing through the microscope lenses, numerous minuscule creatures could be seen by the students. Their instructor explained that a variety of creatures live in pond water, and the creatures on the slides are called "protists." Protists come in a variety of forms and sizes. The instructor continued to explain that some protists are "plant-like" microscopic organisms, while other protists are "animal-like" microscopic organisms. But protists are not considered to be plants or animals; Protists are a distinct classification of life. The students had a magnificent time viewing this ordinarily unseen world.

18
Which of these sentences from the passage shows a shift in the voice?
A.
The instructor continued to explain that some protists are "plant-like" microscopic organisms, while other protists are "animal-like" microscopic organisms.
B.
After filling all of the sample containers, the students returned to their classroom where several microscopes were placed on lab desks by the students.
C.
But protists are not considered to be plants or animals; Protists are a distinct classification of life.
D.
Thankfully, the weather was clear, enabling the students to accomplish their assigned task.