Final answer:
In the given sentence, the subject is 'The teacher' and the verb is 'plans'. The subject indicates who is carrying out the action, while the verb describes the action being planned.
Step-by-step explanation:
In the sentence “The teacher plans to mark the books this evening,” the subject is “The teacher” and the verb is “plans.” The subject of a sentence is the person, place, thing, or idea that is doing or being something. In this case, “The teacher” is the person who is planning an action. The verb is the word that expresses the action or state of being. Here, “plans” indicates what the subject intends to do. This exercise is a great way to understand sentence structure and the function of different parts of speech within a sentence.