Select the option that expresses the given sentence in passive voice.

Teachers love their students.

Students are loved by their teachers.

In the active voice sentence, "Teachers love their students," the subject (teachers) performs the action (love) on the object (students).

To convert the sentence to passive voice, we make the object (students) the subject of the sentence and use the verb "are loved" in the corresponding form. The agent or the doer of the action (teachers) is not mentioned explicitly in the passive voice.

Therefore, the passive voice sentence is: "Students are loved by their teachers."

The other options are incorrect:

1. "Students are being loved by their teachers" also represents the passive voice, but it implies an ongoing or continuous action with the use of the auxiliary verb "being loved." The original sentence does not imply a continuous action, so this option is not suitable.

2. "Students have been loved by their teachers" uses the present perfect tense, which suggests an action that started in the past and continues until the present. However, the original sentence does not convey a sense of continuous action, so this option is not appropriate.

3. "Students will be loved by their teachers" uses the future tense, indicating an action that will happen in the future. While grammatically correct, it changes the tense and does not accurately reflect the present tense of the original sentence.

Therefore, the correct option is: "Students are loved by their teachers."