Hij klaagt over het weer. (He complains about the weather.)
klagen takes "over" (klagen over = to complain about). Example: Hij klaagt over het weer. (He complains about the weather.)
Hij klaagt over het weer. — He complains about the weather. The preposition over is fixed, so it doesn't change with the sentence.
Fixed prepositions come up all over the A2 exam. The platform drills them in real exam tasks, AI-graded across all five DUO sections.