<prompt> Which of the following statements about an amalgam toothcavity preparation is true?The enamel cavosurface margin angle must be 90 degrees.The cavosurface margin should provide for a 90- degree amalgam margin.All prepared walls should converge externally.Retention form for Class Vs can be placed at the DEJ.  <response>: Although the amalgam margin must be 90 degrees, the enamel margin may not be 90 degrees, especially on the occlusal surface. Most walls converge occlusally, but many Class V amalgam preparations have walls that diverge externally. No retention form should be placed at the DEJ; otherwise, the adjacent enamel will be undermined and subject to fracture. 