Correct Phrase Explanation

The phrase 'as well as' is used correctly in the sentence to indicate Gauri's ability to play the keyboard in comparison to her sister. This structure implies that her skill level is comparable or similar to her sister's.

The sentence structure is: Subject + Verb + 'as well as' + Noun/Pronoun.

Example: Gauri can play the keyboard as well as her sister.

Analyzing Incorrect Options

The other options are grammatically incorrect or inappropriate for this context:

• 'as better as': This is incorrect. 'Better' is already a comparative adjective. The correct comparative structure is 'better than'. The 'as...as' structure requires the base form of the adjective (e.g., 'as good as').
• 'as nicest as': This is incorrect. 'Nicest' is a superlative adjective. The 'as...as' structure requires the base form ('nice'), making it 'as nice as'. However, 'nice' is not typically used to describe playing a musical instrument.
• 'as worse as': This is incorrect. 'Worse' is a comparative adjective. The 'as...as' structure requires the base form ('bad' or 'ill'), making it 'as badly as' or 'as poorly as' if comparing negative ability.

Therefore, 'as well as' is the only suitable option for Gauri's keyboard playing comparison.