Which statement BEST describes the operation of a negative-edge-triggered D flip-flop?

• A. the logic level at the d input is transferred to q on ngt of clk.
• B. the q output is always identical to the clk input if the d input is high.
• C. the q output is always identical to the d input when clk = pgt.
• D. the q output is always identical to the d input.