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