Consider the letter reduction series: ATTRIBUTION, TTRIBUTIO, RIBUTIO, IBUTI. Choose from the options the next group of letters that logically follows this pattern.

Introduction / Context:
This is a letter reduction series based on the word ATTRIBUTION. Each term in the series is obtained by deleting characters from the previous term in a systematic way. Recognising how letters are removed from the ends allows us to predict the next resulting substring.

Given Data / Assumptions:

• Series: ATTRIBUTION, TTRIBUTIO, RIBUTIO, IBUTI, ?
• Each step removes one or more letters from the previous term.
• We want to identify how the length and content of the term changes at each step.

Concept / Approach:
First, we compare each term with the one before it and see which letters have been dropped. The pattern is very likely based on removing the first letter, or the first and last letters, to keep the central portion of the word. By tracking this removal pattern, we can find what remains in the next step.

Step-by-Step Solution:
1. Start with ATTRIBUTION. 2. The second term TTRIBUTIO is obtained by dropping the first and last letters of ATTRIBUTION. 3. Original: A T T R I B U T I O N. Dropping A and N leaves: T T R I B U T I O which is TTRIBUTIO. 4. The third term RIBUTIO is formed by dropping the first letter T from TTRIBUTIO. 5. The fourth term IBUTI is formed by dropping the first and last letters from RIBUTIO. 6. Write RIBUTIO clearly: R I B U T I O. Dropping first R and last O leaves: I B U T I which is IBUTI. 7. To obtain the next term from IBUTI, continue the same style of central reduction. 8. IBUTI consists of I B U T I. 9. If we remove the first and last letters I and I, the remaining central part is B U T. 10. Therefore the next term is BUT.

Verification / Alternative check:
List the sequence with lengths: ATTRIBUTION (length 11) TTRIBUTIO (length 9) RIBUTIO (length 7) IBUTI (length 5) BUT (length 3) At each step, the length reduces by 2 (11, 9, 7, 5, 3) which confirms the consistent removal of one letter from each end at alternate steps.

Why Other Options Are Wrong:

• IBU: This still contains the outer I and I, but the pattern requires removing outer letters to get shorter and shorter central strings.
• UT: Length 2 does not follow the length sequence 11, 9, 7, 5, 3.
• UTI: Length 3 matches, but UT I does not represent the inner core correctly removed from IBUTI by dropping both ends.

Common Pitfalls:
Learners may try to interpret the series as random truncations from only one side, but the clear length pattern and central alignment show that letters are symmetrically removed from the start and end. Failing to count the letters and verify the length progression often leads to incorrect guesses.

Final Answer:
The next group of letters in the series is BUT.