To solve this question, we need to choose the correct phrase to complete the sentence: "Gauri said that she can play the keyboard \(\underline{\hspace{2cm}}\) her sister."
This sentence compares Gauri's ability to play the keyboard to that of her sister. The intended meaning is that Gauri can play the keyboard at a similar level or capability as her sister.
Let's analyze the options:
After evaluating the given options, it becomes clear that the correct completion of the sentence is "as well as" because it correctly conveys that Gauri's ability to play the keyboard is equal to that of her sister.
Conclusion: The correct option is "as well as," which accurately completes the sentence meaningfully and grammatically.