<prompt> Translate the following text to EnglishKwa hiyo, NHTSA ilifikia mkataa kwamba mbadala pekee ya kisheria iliyoruhusiwa ilikuwa kuanzisha kiwango cha mwaka wa mfano wa 1998 katika 20.  <response>: Accordingly, NHTSA concluded that the only legally permissible alternative was to establish the model year 1998 standard at 20. 