Solution: Solution: A. Take the right-angle wedge and cube with mass m as the research objects, analyze the stress situation, as shown in figure 1, and obtain from the equilibrium conditions:

The elasticity of the cube in the horizontal direction is N3 = (m+m) g, so A is correct.

B and C study the right-angle wedge and analyze the stress, as shown in Figure 2. According to the equilibrium condition, it is known that the resultant force f of gravity mg and the elastic force N 1 of the wall is equal to the supporting force N4 of M, but opposite in direction, which indicates that:

The elastic force of the wall to m is N 1=mgtanα, and the elastic force of the cube to the right wedge is n4 = mgsin α.

As a whole, the elastic force of the wall on the cube N2 = N 1 = mg tan α. So, B is right and C is wrong.

D, according to Newton's third law, the elastic force of right-angle chopping on the wall is n 1'= n 1 = mg tanα, so d is wrong.

So choose AB