Select the combination of letters that when sequentially placed in the blanks of the given series will complete the series.
p _ t b c p r _ b c _ r t b _ p _ t _ c

A

r, c, p, b, t, r

B

r, p, c, t, b, r

C

r, t, p, c, r, b

D

r, p, t, r, b, c