Questions & Answers about Wir parken das Auto auf der Straße.
What case is das Auto in, and why?
“das Auto” is the direct object of the verb parken, so it takes the accusative case. Since Auto is a neuter noun, its accusative singular article remains das.
Why is it auf der Straße and not auf die Straße?
The preposition auf can govern either dative (for location: “where”) or accusative (for direction: “onto”). Here it describes the location of the parked car, so you use the dative case. Straße is feminine, and its dative singular article is der, giving auf der Straße.
Why is the article for Straße der and not die?
Straße is feminine. In nominative or accusative singular the article is die, but when a feminine noun is used with a dative preposition (here auf indicating location), its article changes to der.
Could we use in der Straße instead of auf der Straße?
You could say in der Straße, but that usually implies being inside or between the buildings lining the street (e.g. “in the street itself,” maybe standing among traffic). auf der Straße is the normal way to say “on the street” in the sense of parking alongside it. Another alternative is an der Straße (“by the street”).