Select the option that contains the correctly spelt standard English word among the four given choices.

Introduction / Context:
Spelling based questions are a common feature of competitive English tests because they assess a candidate's familiarity with standard written English. In this question, the learner must identify which one of the four options is spelt correctly according to accepted usage. Such items not only test memory but also reading habits, since repeated exposure to correct forms in books and newspapers usually strengthens spelling skills.

Given Data / Assumptions:

Four similar looking words are given as options.
Only one is a correctly spelt English word in everyday usage.
The words resemble real English words such as revolver, culpable, vegetate, and rhythmic.
The learner must choose the option that matches the correct dictionary form.

Concept / Approach:

Words in spelling questions are often near misses of standard vocabulary, with one or two letters changed, added, or omitted.

Here, we check each option against the known correct forms.

"Culpable" is a known English adjective meaning "deserving blame".

The other three options show suspicious letter combinations that do not match the usual patterns.

Step-by-Step Solution:
Step 1: Look at option a, "rewolver". The correct word referring to a type of gun is "revolver", not "rewolver"; the extra "w" makes this spelling wrong. Step 2: Look at option b, "culpable". This is a recognized English adjective that means deserving blame or censure. It appears frequently in legal and moral contexts, and the spelling looks standard. Step 3: Look at option c, "vagetate". This appears to be a distorted version of "vegetate" which means to lead a dull, inactive life. The correct spelling uses "vege" rather than "vage". Step 4: Look at option d, "rhythmmic". The correct word meaning having rhythm is "rhythmic" with only one "m" in the middle, not "rhythmmic". Step 5: Since only option b matches a correct, standard dictionary spelling, select "culpable" as the correct answer.

Verification / Alternative check:
Consulting any standard English dictionary shows entries for "culpable" and "revolver" but not for "rewolver". Similarly, the dictionary lists "vegetate" and "rhythmic", confirming that "vagetate" and "rhythmmic" are incorrect spellings. Therefore, cross checking with known correct spellings supports option b as the only valid choice.

Why Other Options Are Wrong:
Option a is wrong because it inserts an unnecessary "w", creating a non standard form that does not appear in reputable dictionaries. Option c is wrong because it replaces "vege" with "vage", which is not the correct root for the verb "to vegetate". Option d is wrong because it doubles the "m" and produces "rhythmmic" instead of the accepted "rhythmic".

Common Pitfalls:
Test takers sometimes rely on how a word sounds rather than how it is conventionally written, which can mislead them when extra letters appear. Another common mistake is to be distracted by unusual looking combinations like "rhythmmic" because the base word "rhythm" already has a double consonant feel. To improve accuracy, students should read widely and pay attention to how words appear in print, not just how they sound.

Final Answer:
The correct answer is: culpable.