19. The projection pattern of the three views is that the main view is the same length as the top view; The main view is at the same height as the left view. The top view is as wide as the left view.

20. The parts have dimensions in three directions: length, width, and height. The main view can reflect the length and height of the parts, the top view can only reflect the length and width of the parts, and the left view can only reflect the height and width of the parts.

21. The parts have six orientations: up, down, left, right, front, and back. In the main view, only the up, down, left, and right orientations of the parts can be reflected. In the top view, only the front, back, left, and right orientations of the parts can be reflected. In the left view, only the up, down, front, and back orientations of the parts can be reflected.

22. There are a total of three basic views, named Main View, Top View, and Left View.

23. In addition to the basic view, there are three types of views: top view, right view, and rear view.

24. According to the size of the cutting range, the cutting view can be divided into three types: full cutting view, half cutting view, and partial cutting view.