Select the combination of letters that when sequentially placed in the blanks will create a repetitive pattern.

_ s t u _ v u t s _ r s t _ v v u _ s r

Given: _ s t u _ v u t s _ r s t _ v v u _ s r

Now, we check each options.

Option (a): r v r u t 

​r s t u v v u t s r / r s t u v v u t s r

Option (b): t u r v r

​t s t u u v u t s r /  s t v v v u r s r

​Not Following a logical repeating pattern

Option (c): t s u v r

Not Following a logical repeating pattern​

Option (d): r v u s t

​r s t u v v u t s u / r s t s v v u t s r

Not Following a logical repeating pattern​

So, the correct pattern follow is: r s t u v v u t s r

Thus, correct option is (a).