Explanation:

Let's analyze the series:

_ u v w u v _ w v t u w _ u v w u v _ w v _ u w

Let’s fill each blank with the same letter and check options:

- Option 1: t t t t t

- Filling: t u v w u v t w v t u w t u v w u v t w v t u w

- Sequence looks repetitive but breaks the visible patterns among u, v, w.

- Option 2: t u t u t

- Filling: t u v w u v u w v t u w t u v w u v u w v t u w

- Loss of repetition, doesn't fit the logical sequence.

- Option 3: t v w t t

- Filling: t u v w u v v w v t u w w u v w u v t w v t u w

- Creates double v, double w, breaking the repeating block u v w.

- Option 4: t t u t v

- Filling: t u v w u v t w v u u w t u v w u v t w v v u w

- Disturbs the order, doesn't continue the cycle.

- Observing, the sequence 'u v w' repeats often, but between, there's always a 't' before or after. Option 1 consistently places 't' to bridge between cycles, maintaining uniformity.

Correct answer:

Option 1: t t t t t