In a Lexical Decision Task, a Researcher Finds No Effect

In a lexical decision task, a researcher finds no effect of priming. Which of the following statements is a plausible explanation for this?

A) The researcher neglected to tell the participants that some of the test words had been recently encountered.
B) Some of the test words were high in frequency, but others were quite low in frequency.
C) When the priming words were first presented, participants failed to pay attention to the meaning of the words.
D) Participants initially heard the words via a tape-recorded list but were tested under conditions where they were visually presented the list.