Option C. The best revision of the underlined portion of the sentence would be "requiring us to wear uniforms is unnecessary".
Explanation:
When writing a letter to an authority figure, like the principal of your school, it is important to conduct the letter with utmost respect, therefore the use of vocabulary has to match the tone of the letter. Using words such as "ridiculous" in a formal letter may be seen as disrespectful, undermining the goal of the letter. Instead of putting in the letter a statement such as "making us wear uniforms is ridiculous", better write "requiring us to wear uniforms is unnecessary".
