Learn Hardcore German: Die Stadt erweitert das U-Bahn-Netz, um Staus zu verhindern. - The city is expanding the subway network in order to prevent traffic jams.

Erweitert is the third-person singular present form of the verb erweitern, which means “to expand” or “to extend.” In this sentence, it tells us what the subject (“Die Stadt”) is doing.

Why is das U-Bahn-Netz in the accusative case?

Erweitern is a transitive verb—it takes a direct object in the accusative. So das U-Bahn-Netz (the subway network) is the thing being expanded, hence accusative.

Why is there a comma before um?

German requires a comma before an um … zu purpose clause. It marks the boundary between the main clause and the infinitive clause of purpose.

How does the um … zu construction work?

This structure expresses purpose and corresponds to “in order to” in English. You form it with: • um
• zu + infinitive verb
The whole um … zu phrase comes at the end of the sentence.

Why is Staus plural and what case is it in?

Staus is the plural of Stau (“traffic jam”) because the sentence refers to traffic jams in general. In the um … zu clause verhindern takes its object in the accusative, so Staus is accusative plural.

What gender is Stadt, and why does it have the article die?

Stadt is a feminine noun in German. In the nominative singular, the definite article is die.

Why are there hyphens in U-Bahn-Netz?

“U-Bahn” itself is a shortened compound of Untergrundbahn (underground railway). When it combines with Netz (network), hyphens keep the parts clear and readable: U-Bahn-Netz.

Is verhindern the same as vermeiden?

They’re related but not identical:
• verhindern = “to prevent” (stop something from happening)
• vermeiden = “to avoid” (keep away from something)
Here the city actively prevents traffic jams by expanding the network.