sentences:  Two well-known and frequently studied morphophonological variables are T/D deletion, the optional deletion of the sound /t/ or /d/ at the end of a word, as in "I kep' walking" (Wolfram 1969; Labov et al.1968); and the ING variable, the optional pronunciation of "-ing" at the end of a word as "-in"', as in "I kept walkin'" (e.g.Fisher 1958; Labov 1966/1982; Trudgill 1974).