Er is gebrek aan personeel. (There is a lack of staff.)
gebrek takes "aan" (gebrek aan = lack of). Example: Er is gebrek aan personeel. (There is a lack of staff.)
Er is gebrek aan personeel. — There is a lack of staff. 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.