Final answer:
The sentence 'The students' questions are always answered by the teacher' is in passive voice because the subject receives the action performed by someone else.
Step-by-step explanation:
The sentence in question, 'The students' questions are always answered by the teacher,' is in passive voice. To determine if a sentence is passive, we look at whether the subject of the sentence is performing the action or if the action is being performed on the subject. In this case, 'the students' questions' (the subject) are not doing the action—instead they are receiving the action of being answered by someone else (the teacher). This structure fits the passive voice characteristics: the subject is acted upon, there is a form of 'be' (in this case, 'are'), and the preposition 'by' followed by a noun phrase ('by the teacher') can be found or can be added.
In comparison, an active voice would place the subject as the doer of the action, such as in 'The teacher always answers the students’ questions.'