The correct option is: for thousands of years, we have been making maps to represent the physical world.
The nominative case is present when a noun or noun phrase is used as the subject of a verb. For example, "the boy saw her", "the boy" is a noun phrase in the nominative case.
In the question, you have to find a pronoun in the nominative case. So, a pronoun like I, you, we, they, he, she or it should be used as the subject to a verb. In the sentence "for thousands of years, we have been making maps to represent the physical world", "we" is the pronoun that acts as a subject to the verb phrase "have been making".