The Consumer Product Safety Commission.$($CPSC$)$ proposes a new rule requiring battery manufacturers like TIP Tech to affix a warning label to all of their products. The CPSC publishes a notice of the proposed rule and then holds a public hearing in which witnesses testify both in favor of and against the proposed rule. After the CPSC makes an official transcript of the hearing, it publishes the final rule in the 'Federal Register. Which form of rule making was used?