According to the exploration of unit 1 "observing objects (3)" in the second volume of fifth grade mathematics, the fifth grade should have three views, which are the contents that need to be mastered in the first volume of ninth grade.

Three views refer to orthographic engineering drawings (three basic views: front view, top view and left view) that can correctly reflect the length, width and height of objects, and are abstract expressions of the geometric shapes of objects in the engineering field.