The best response would be, "What does business casual mean here?". Since business casual is an objective term and may differ from company to company.
Business casual is defined as a dress code that is generally considered casual but includes smart components of a proper lounge suit, mainly adopted for white-collar jobs.
It is difficult to define business casual precisely since it is an objective term and can have different meanings for different organizations.
Therefore, the response to the statement of the boss would be asking the meaning of business casual as per the company.
Hence the correct option is C.
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