Final answer:
The command to improve readability of a worksheet when long labels are required is 'B. Wrap Text'. This function allows text to be visible within the cell, aiding in maintaining the worksheet's legibility and appearance.
Step-by-step explanation:
When long labels are required to improve readability of a worksheet, the command you can use is B. Wrap Text. This feature adjusts the height of the rows and/or the width of the column to fit the text within a cell, ensuring that all the content is visible without having to widen the columns excessively. This makes it easier to read the data and enhances the appearance of the worksheet.
In contrast, A. Merge & Center combines multiple cells into one and centers the content, which can be useful for titles but not necessarily for long labels. C. Conditional Formatting allows you to format cells based on their values, which doesn't directly relate to improving readability of long text. Finally, D. Sort & Filter which you correctly identified as the wrong answer, is a tool for organizing data rather than dealing with text length issues.