Question: According to the ASA criterion, which of the following needs to be added to the diagram above to show that $\triangle MNO \cong \triangle PQR$?
A. tick marks showing that $\angle N \cong \angle P$
B. tick marks showing that $\angle M \cong \angle P$
C. tick marks showing that $\angle N \cong \angle Q$
D. tick marks showing that $MO \cong PR$
1. **Problem Statement:** We need to determine which additional congruence mark must be added to the diagram to prove that $\triangle MNO \cong \triangle PQR$ using the ASA (Angle-Side-Angle) criterion.
2. **ASA Criterion Explanation:** The ASA criterion states that two triangles are congruent if two angles and the included side of one triangle are congruent to two angles and the included side of another triangle.
3. **Given Information:**
- In $\triangle MNO$, $\angle O$ is marked congruent.
- Side $ON$ has a tick mark indicating congruence.
- In $\triangle PQR$, $\angle R$ is marked congruent.
- Side $QR$ has a tick mark indicating congruence.
4. **What is Missing?**
- To apply ASA, we need two pairs of congruent angles and the included side between them.
- Currently, we have $\angle O \cong \angle R$ and side $ON \cong QR$.
- The missing pair is the congruence between $\angle N$ and $\angle Q$ to complete the ASA pattern.
5. **Conclusion:** The correct addition is tick marks showing that $\angle N \cong \angle Q$.
**Final answer:** C. tick marks showing that $\angle N \cong \angle Q$