Select the option that represents the letters that, when sequentially placed from left to right in the blanks below, will complete the letter series.
t _ r a s _ t _ s _ a _ _ _ t _ r _ s r t

A

s r t r a r t s a

B

s r a r s r t s a

C

s r t r s r t s t

D

s r t r s r t s a