Vertical angles must:Check all that apply.A.be congruent.B.be a linear pair.C.have the same vertex.D.be adjacent.

To solve the question regarding the properties of vertical angles, we need to evaluate the statements provided.

1. Congruence: Vertical angles are always congruent. This is a key property of vertical angles, formed by two intersecting lines. When two lines cross, the opposite angles are equal in measure.

2. Linear Pair: Vertical angles do not form a linear pair. A linear pair consists of two adjacent angles that add up to 180 degrees; vertical angles are not adjacent, hence this statement is false.

3. Same Vertex: Vertical angles are formed at the intersection of two lines and therefore share the same vertex. This is indeed a property of vertical angles.

4. Adjacency: Vertical angles are not adjacent angles. They are opposite each other and do not share a side.

Conclusion:

Considering the evaluations above, the statements that apply to vertical angles are:

• A. be congruent.
• C. have the same vertex.

Final Answer: A and C are correct. Vertical angles must be congruent and have the same vertex.