1. The problem asks to identify the type of symmetry that involves a rotation isometry around a center point combined with mirror lines through the center point. 2. The key terms are: - Rotation isometry around a center point with $n$-fold rotational symmetry. - Reflectional symmetry (mirror lines through the center). 3. Let's analyze the options: - Spiral: Typically involves rotation but no reflection symmetry. - Dihedral: Has $n$-fold rotational symmetry and reflectional symmetry through mirror lines. - Cyclic: Has $n$-fold rotational symmetry but no reflectional symmetry. - Rosette: Usually involves multiple symmetries but not necessarily reflectional symmetry through the center. 4. The correct answer is the dihedral group, which combines $n$-fold rotational symmetry and reflectional symmetry through mirror lines intersecting at the center. Final answer: Option B, Dihedral.