Hij stopt met roken. (He stops smoking.)
stoppen takes "met" (stoppen met = to stop (doing)). Example: Hij stopt met roken. (He stops smoking.)
Hij stopt met roken. — He stops smoking. The preposition met 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.