Fill in the blanks with letters to complete the repeating pattern. Pattern: _ stt _ tt _ tts _

Introduction / Context:
This problem asks you to insert letters into four blanks so that the entire string follows a consistent, repeating pattern of s and t clusters. Such questions test visual pattern recognition and string sequence reasoning frequently used in competitive exams.

Given Data / Assumptions:

• Template: _ stt _ tt _ tts _
• Options provide four letters to fill the four blanks in order.
• Only one option should create a smooth, internally consistent repetition.

Concept / Approach:
Identify recurring blocks such as "stt", "tt", and "tts". The goal is to choose letters so that adjacencies form sensible clusters without creating impossible doubles or breaking a growing/alternating motif.

Step-by-Step Solution:
Consider option "tsst" mapped to the four blanks sequentially. Substitute: t stt s tt s tts t. Now scan clusters: we see a plausible alternation of single letters around stable blocks "stt", "tt", and "tts". No illegal or contradictory junctions arise. Testing other options leads to awkward or broken transitions like stranded doubles or inconsistent growth in cluster sizes.

Verification / Alternative check:
Re-check by inserting each of the other options. They introduce either repeated conflicts (e.g., forced tt at odd junctions) or disrupt the visible rhythm of the base blocks. "tsst" remains the smoothest continuation.

Why Other Options Are Wrong:
tsts: Produces clashing joins that break the emergent cadence around “tt” and “tts”. ttst: Forces heavy tt merges in places that destroy the staggered feel of the sequence. sstt: Introduces double s joins that do not align with the recurring clusters.

Common Pitfalls:
Judging only locally (one blank at a time) instead of checking the global effect across all clusters.

Final Answer:
tsst