Wij nemen deel aan de cursus. (We take part in the course.)
deelnemen takes "aan" (deelnemen aan = to take part in). Example: Wij nemen deel aan de cursus. (We take part in the course.)
Wij nemen deel aan de cursus. — We take part in the course. The preposition aan 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.