Which one of the following statements accurately reflects a rule for the use of abbreviations? a. the symbol "$" may stand alone in a sentence, because it's a familiar symbol. b. the abbreviations "p. m." and "p. m. can be used interchangeably within a document c. the abbreviation "ph. d." may be written only in conjunction with a proper name. d. the abbreviation "b. c." should be associated with a number, such as 44 b. c