讲解这道题---**Question 3**
**Question Stem:**
As shown in the figure, in the right triangular prism ABC-A₁B₁C₁, ∠BAC = 90°, AB = AC = 2. Points M and N are the midpoints of A₁C₁ and A₁B₁ respectively.
**(1) Prove:** MN // plane BB₁C₁C;
**(2) If:** CM ⊥ MN, find the volume of the triangular pyramid M-NAC.
**Chart/Diagram Description:**
* **Type:** Geometric figure, specifically a right triangular prism.
* **Main Elements:**
* The prism is named ABC-A₁B₁C₁, where ABC is the bottom base and A₁B₁C₁ is the top base.
* **Vertices:** A, B, C, A₁, B₁, C₁.
* **Edges:**
* Solid lines: A₁B₁, B₁C₁, C₁A₁ (top base edges), BB₁, CC₁ (lateral edges), BC (bottom base edge), MN, CM, CN (internal connecting lines).
* Dashed lines: AA₁, AB, AC (bottom base edges and lateral edge), AN, AM (internal connecting lines).
* **Points:**
* M is located on the edge A₁C₁.
* N is located on the edge A₁B₁.
* **Connectivity:**
* Line segment MN connects point M and point N.
* Line segment CM connects point C and point M.
* Line segment CN connects point C and point N.
* Line segment AN connects point A and point N.
* Line segment AM connects point A and point M.
* **Implied Geometry based on text:**
* The base triangle ABC is a right-angled isosceles triangle with the right angle at A (∠BAC = 90°).
* Sides AB and AC have length 2 (AB = AC = 2).
* The prism is a "right" prism, meaning the lateral edges (AA₁, BB₁, CC₁) are perpendicular to the bases.
* M is the midpoint of A₁C₁.
* N is the midpoint of A₁B₁.