The full name determines the answer.
All four German answers begin with “Sozial-”. Recognising that beginning alone is therefore not enough. The exact correct word is “Sozialdemokratische”.
In the abbreviation, S stands for the first part, P for Partei and D for Deutschlands. Here D therefore belongs to the final word, unlike CDU and FDP.

The other three answers
Each incorrect answer replaces the first word.
Socialist Party of Germany
“Sozialistische”, meaning socialist, is not the official first part of the name. This question requires the exact designation.
Social Political Party of Germany
“Sozialpolitische” sounds related in topic but is not part of the expanded name SPD.
Socially Just Party of Germany
“Sozialgerechte”, meaning socially just, is also not the party name. A generally positive-sounding quality does not replace an official name.
A name does not summarise every political position.
The question asks neither for support for a party nor a comparison of programmes. It tests whether the abbreviation matches the fixed name.
“Deutschlands” is the genitive form, meaning “of Germany”. It does not mean that everyone in Germany belongs to the party.
Social Democratic Party of Germany · SPD · Official name ↗Social Democratic – Party – of Germany.
Learn the first word in full; it distinguishes all four answers.
Three words for this question
- sozialdemokratischsocial democratic
- The description relating to social democracy within the fixed party name.
- der Parteinameparty name
- The official designation of a political party.
- Deutschlandsof Germany
- A genitive form that is part of the full name here.
