Language Research Suggests That There Are/is

Language research suggests that there are/is:

A) One phonological store involved in the phonological loop-the input buffer
B) Three phonological stores involved in the phonological loop-the semantic conceptualization store, the input buffer, and the output buffer
C) Four phonological stores involved in the phonological loop-the semantic store, the conceptualization store, the input buffer, and the output buffer
D) Two phonological stores involved in the phonological loop-the input buffer and the output buffer
E) An unlimited number of phonological stores involved in the phonological loop