The correct answer is A. When people enter the harbor, their vision fixes on this marvelous symbol of liberty.
Step-by-step explanation:
The verb to be used in the sentence "people are... they are" is not considered an action verb because this is a linking verb, which means it describes a state or describes the subject by linking this to other words. This is the opposite of an action verb such as go, eat, see, etc. because these all describe specific actions performed by the subject. In this context, the best option to use action verbs is the first option because this replaces the verb to be by the action verbs "enter" and "fix."