“Kreis” and “Landkreis” refer to the same level here.
The question says Landkreis, while the authority calls itself Kreis Nordfriesland. That wording difference does not make the answer wrong. It refers to a local territorial unit above the individual municipalities.
Husum is the location of the county administration. Kiel, by contrast, is the capital of the whole federal state. Keeping those levels separate avoids confusing the county with its administrative town or Husum with the state capital.
The other three answers
The other counties are in other federal states.
Ammerland
Ammerland is in Niedersachsen. The fact that both states are in northern Germany does not make their counties interchangeable.
Mecklenburgische Seenplatte
Mecklenburgische Seenplatte is a county in Mecklenburg-Vorpommern. Schleswig-Holstein’s neighbour is a separate federal state.
Rhein-Sieg-Kreis
Rhein-Sieg-Kreis is in Nordrhein-Westfalen. It is not a Schleswig-Holstein county.
A similar region is not an administrative classification.
A name may suggest a coast, landscape or history. What matters here is the county’s present federal-state classification. The county authority and its legal basis are more reliable than a guess from the name.
The answer requires neither the number of municipalities nor population figures. The three levels of town, county and state are enough to understand the question.
Principal statute, section 1 · Nordfriesland county ↗Nordfriesland → Schleswig-Holstein. Administrative seat → Husum.
Distinguish Husum as county town from Kiel as state capital.
Three words for this question
- der Kreiscounty
- A local territorial body containing several municipalities.
- der Amtssitzadministrative seat
- The legally designated location of an authority.
- die Hauptsatzungprincipal statute
- Fundamental local rules on organisation and administration.