The correct answer is D. The 200-year party will be lots of fun as the whole town rocks the boardwalk.
Explanation
Informal language is a style of language used in an informal environment such as that used with family members, classmates, and friends, in which technical or specialized terms should not be used, on the contrary, a simpler, natural, every day language is used. According to the above, it can be inferred that the sentence "The 200-year party will be lots of fun as the whole town rocks the boardwalk" uses informal language because everyone can understand the message and does not require knowledge of specialized terms. Also, use simple, everyday language such as "lot of fun". So the answer is D.
