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The fourth grade mathematics classroom exercise book volume 1 answer C version Unit 2 Lesson 2 Know the vertical and draw the vertical line.
Answer: 1, all have right angles.

2. Omission

3. The segment between two points is the shortest.

4、( 1)4

(2) Vertical vertical

5. Omission

6. Omission

7.AO and BO are perpendicular to each other, DO and CO are perpendicular to each other, AB and BC are perpendicular to each other, AD and DC are perpendicular to each other, and so on.