Word puzzle: find the 5-letter English word of the form _RUS_ that begins and ends with the same letter.

Introduction / Context:
This riddle is a simple pattern recognition problem with English spelling. We are told that a five letter word looks like _RUS_, meaning that its second, third and fourth letters are R, U and S, and that the first and last letters are the same. Word shape puzzles like this are common in verbal reasoning sections of competitive exams and help train attention to spelling patterns and constraints.

Given Data / Assumptions:

• The word has exactly five letters.
• The pattern is _ R U S _, so positions two, three and four are R, U and S.
• The first and fifth letters are identical.
• The answer must be a standard English word, not a name or abbreviation.
• Exactly one option satisfies both the pattern and the equal first and last letter condition.

Concept / Approach:
We can write the word as X R U S X, where X is some letter that appears in both the first and last positions. The easiest way is to test each answer option against this structure. If the letters in the second, third and fourth positions are R, U and S and the first and last letters match, that option fits the description. Otherwise, it is a distractor. This direct checking approach is fast and reliable.

Step-by-Step Solution:
Write the pattern as X R U S X, with X the same letter at both ends. Check trust: spelling is t r u s t. Positions: 1 = t, 2 = r, 3 = u, 4 = s, 5 = t. Letters in positions 2, 3 and 4 are r, u, s exactly as required. First and last letters are both t, so trust matches the full condition.

Verification / Alternative check:
Now quickly test the other options. Crust is c r u s t: second to fourth letters are r, u, s but the first letter is c and the last is t, so the ends are not the same. Truss is t r u s s: the letters r, u, s appear, but the first letter t and the last letter s differ. Brush is b r u s h: again positions two to four are r, u, s, but the word starts with b and ends with h. Only trust has the required pattern and identical first and last letters.

Why Other Options Are Wrong:
Crust, truss and brush all satisfy part of the pattern because they contain the sequence r u s in the middle, but they all fail the final requirement that the first and last letters must be the same. They are included to tempt quick guesses from learners who only look at the internal letters and forget to check the endpoints of the word shape.

Common Pitfalls:
Many people see r u s and rush to select any familiar word containing that sequence without verifying the edge condition. Others misinterpret the underscore notation and assume it means any number of letters rather than exactly one letter at each end. To avoid these mistakes in similar puzzles, always rewrite the pattern explicitly with positional labels and test each candidate word carefully against every constraint given in the riddle.

Final Answer:
The required 5 letter word is trust.