Grammar Correction: Skill Proficiency Phrase

The question asks to find the correct phrase to replace "in dancing" in the sentence "She is good in dancing." This requires understanding the standard English prepositional phrase used to denote skill or proficiency.

Identifying the Correct Idiom

The standard and grammatically correct way to express proficiency in an activity or skill in English is using the structure "good at + [activity/skill]". The activity is typically expressed using the gerund form (the '-ing' form of a verb acting as a noun).

Evaluating the Options

• Option 1: at dance - While "at" is the correct preposition, "dance" is the base noun. The idiomatic structure prefers the gerund form for activities.
• Option 2: with dancing - The phrase "good with" is generally used for interacting with people (e.g., "good with children") or handling objects (e.g., "good with tools"), not for expressing skill level.
• Option 3: at dancing - This option correctly uses the preposition "at" followed by the gerund "dancing", matching the standard idiom for expressing skill proficiency. Example: "She is good at swimming."
• Option 4: on dancing - The preposition "on" is not used with "good" to denote skill in activities.

The original phrase "good in dancing" is a common error, sometimes used for academic subjects ("good in math"), but "good at" is preferred for skills and activities like dancing.

Final Choice

Option 3, "at dancing", is the most suitable and grammatically correct replacement, forming the standard idiomatic phrase "good at dancing".