1. The difficulty of the first unit lies in understanding the characteristics of a circle, understanding the connection between mathematics and daily life, understanding that a straight line proportional to its diameter is the symmetry axis of a circle, understanding the significance of pi, and realizing the mathematical idea of turning a curve into a straight line.

2. The difficulty of the third element is that it can determine the number range of cubes needed to construct this three-dimensional figure according to the shape of the plane figure observed in the given two directions. Need students' three-dimensional thinking.