Fill in the blank with the most appropriate preposition. Ankita is disgusted _____ the habit of her brother.

Introduction / Context:
This is a common preposition-usage question that checks whether you know which preposition correctly follows certain adjectives in standard English. The sentence given is “Ankita is disgusted _____ the habit of her brother.” Many exam questions focus on such adjective–preposition combinations because they are often memorised through exposure rather than through pure rule-learning. Knowing them improves both written and spoken English, especially in formal contexts such as competitive examinations and interviews.

Given Data / Assumptions:

The adjective is “disgusted”.
The noun phrase that follows is “the habit of her brother”.
We must select the preposition that naturally and correctly links “disgusted” with the cause of her feeling.
The options are “with”, “at”, “of” and “on”.

Concept / Approach:
In standard English, when someone feels disgust or strong disapproval because of a person or that person's behaviour, the common collocation is “disgusted with” that person or “disgusted with” that habit. Another acceptable pattern is “disgusted at” something shocking, but the most natural and widely used form with a habitual behaviour is “disgusted with someone / with someone's habit”. Because we are referring to the habit of her brother, the preposition “with” is the best choice here to show strong disapproval directed at the brother's habit.

Step-by-Step Solution:
Step 1: Identify the adjective that demands a specific preposition: “disgusted”. Step 2: Identify what is causing the disgust: “the habit of her brother”. Step 3: Recall common collocations: we say “disgusted with his behaviour”, “disgusted with her attitude” etc. Step 4: Try each option in the sentence: “disgusted with the habit”, “disgusted at the habit”, “disgusted of the habit”, “disgusted on the habit”. Step 5: “Disgusted with the habit” sounds natural and idiomatic; “disgusted at the habit” is less natural in this context; “disgusted of” and “disgusted on” are incorrect. Step 6: Choose “with” as the correct preposition.

Verification / Alternative check:
Look at examples from standard usage: “She is disgusted with his rude remarks.”, “They were disgusted with the corruption in the system.” In each case, the preposition “with” connects the feeling of disgust to the object that causes it. If you substitute “at”, the sentences sound less natural and are rarely used in modern standard English with this structure. Therefore, “Ankita is disgusted with the habit of her brother” is the most appropriate and exam-safe formulation.

Why Other Options Are Wrong:
At: “Disgusted at” can sometimes be used with events or situations (“disgusted at the news”), but “disgusted with” is preferred when talking about habits or personal behaviour. Here, “with” is clearly better with “the habit of her brother”.
Of: “Disgusted of” is ungrammatical in standard English; the adjective “disgusted” does not take “of” in this meaning.
On: “Disgusted on” is incorrect; “on” does not collocate with “disgusted” to express this emotion.

Common Pitfalls:
Students often confuse “disgusted at” and “disgusted with”, or try to translate directly from their mother tongue, creating incorrect preposition choices. The safest strategy is to learn common adjective–preposition pairs as fixed expressions: “angry with”, “angry at”, “pleased with”, “tired of”, “interested in”, “disgusted with”. Regular reading of good English texts and noting such combinations will make these patterns feel natural over time, which is very helpful for cloze tests and sentence-correction questions in competitive exams.

Final Answer:
Correct answer: with.