C# windows phone XNA game

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C#

Mobile

Windows-Phone-7

XNA

Hello, I'm trying to draw a terrain using the points given by this function:

public static Level GenerateDummyLevel(int width, int height)
        {
            Level level = new Level();

            bool up = false;

            for (int i = 0; i <= width; i += 20)
            {

                level.Terrain.Add(new Vector2(i, height / 2 + (up ? -10 : 10)));

                up = !up;
            }

            return level;
        }

and this function draws the terrain:

public void Draw(GraphicsDeviceManager graphics, SpriteBatch spriteBatch, PrimitiveBatch primitiveBatch)
{
    // Draw sprites
    this.Lander.Draw(graphics, spriteBatch, primitiveBatch);

    // Draw terrain
    primitiveBatch.Begin(PrimitiveType.TriangleList);

    if (this.Terrain.Count > 1)
    {
        for (int i = 0; i < (this.Terrain.Count - 1); i++)
        {
            primitiveBatch.AddVertex(new Vector2(this.Terrain[i].X, this.Terrain[i].Y), Color.Black);
            primitiveBatch.AddVertex(new Vector2(this.Terrain[i + 1].X, graphics.PreferredBackBufferHeight), Color.Black);
            primitiveBatch.AddVertex(new Vector2(this.Terrain[i].X, graphics.PreferredBackBufferHeight), Color.Black);


            primitiveBatch.AddVertex(new Vector2(this.Terrain[i].X, this.Terrain[i].Y), Color.Black);
            primitiveBatch.AddVertex(new Vector2(this.Terrain[i + 1].X, this.Terrain[i + 1].Y), Color.Black);
            primitiveBatch.AddVertex(new Vector2(this.Terrain[i + 1].X, graphics.PreferredBackBufferHeight), Color.Black);

        }
    }

    primitiveBatch.End();

}

The terrain drawn by this function begins from the bottom of screen and ends in the middle how can i start the terrain from the top of the screen instead of the bottom? Is there any way to simply mirror the terrain along x-axis?