In the letter series TER_TE_S_ER_, which set of letters, when placed sequentially in the blanks, will complete the series as a repeated block?

Introduction / Context:
The question presents a partially filled letter series TER_TE_S_ER_ and asks which four letter set, inserted in the blanks from left to right, creates a regular pattern. The visible fragments suggest that a short word-like block might be repeating, which is a very common construction in alphabet test questions.

Given Data / Assumptions:

• Template with blanks labelled: T E R x1 T E x2 S x3 E R x4.
• There are four blanks x1 to x4.
• Options: TERT, STTT, STRS, SRTS.
• We expect a repeated block of equal length across the entire series.

Concept / Approach:
We aim to see if the completed string can be broken into identical blocks of four letters. The partial pattern TER_ at the beginning strongly hints at the block TERS. By choosing the correct letters for x1, x2, x3, and x4, we want to obtain exactly TERS repeated three times. That would provide both simplicity and regularity, which is typical of exam style patterns.

Step-by-Step Solution:
Step 1: Write the template explicitly: T E R x1 T E x2 S x3 E R x4. Step 2: Try option D, SRTS, which gives x1 S, x2 R, x3 T, x4 S. Step 3: Substitute these into the template to get: T E R S T E R S T E R S. Step 4: Group the series into blocks of four letters: TERS | TERS | TERS. Step 5: Each block is identical and equal to the word TERS, so the whole series is a clean repetition of the same block.

Verification / Alternative check:
Check other options briefly. With TERT you get TERT followed by a different group, which breaks the repeated block idea. STTT and STRS produce mixed groups where the second and third blocks differ from the first. Only SRTS makes the sequence TERS TERS TERS, which is completely regular and clearly intended.

Why Other Options Are Wrong:
TERT would give the first four letters as TERT, but later letters would not group into identical blocks. STTT leads to blocks that are not the same from left to right. STRS produces inconsistencies in the middle of the sequence and destroys the neat TERS repetition. Since the visible letters TER at the beginning and the ER later in the series strongly hint at TERS, any completion that does not yield exactly TERS repeated is less plausible.

Common Pitfalls:
Some candidates focus on local fits around a single blank and choose an option that seems to correct only the first gap. Others search for numeric progressions in letter positions even when the structure is obviously word-like. For such series, it is better to look for repeating blocks and check whether the entire string can be partitioned into equal segments.

Final Answer:
The set of letters that completes the series as TERS repeated three times is SRTS.