Which of the following statements is correct for the illustrated circuit?

A.'R1', 'R2', and 'R3' are connected in series.
B.'R1', 'R2', and 'R3' are connected in parallel.
C.The voltages measured across 'R1', 'R2', and 'R3' are equal.
D.The total resistance equals 1/R1 + 1/R2 + 1/R3.