Complex sentence: Foams composed of soap films obey Plateau's laws, which require either three or four soap films to meet at each vertex, at 120 ° or the tetrahedral angle of about 109.5 °, respectively.
Split into simpler sentences: Foams composed of soap films obey Plateau's laws. These require either three or four soap films to meet at each vertex, at 120 ° or the tetrahedral angle of about 109.5 °, respectively.