Poetry in every language celebrates beauty and truth-

- ক. So does art: This option maintains parallelism and effectively completes the sentence by expressing that art, like poetry, also celebrates beauty and truth.

- খ. So as art: This option, while somewhat close, is not as commonly used in this context. The more idiomatic construction is "So does art."

- গ. As well as art: This choice introduces a slight deviation in meaning. "As well as" is often used to add information, suggesting an additive relationship rather than a parallel one. It slightly changes the emphasis of the sentence.

- ঘ. Why not art?: This option introduces a different tone and structure, not maintaining the parallelism of the original sentence. It also doesn't convey the idea of art celebrating beauty and truth in the same way as the other options.

Therefore, the rule here is to select the option that maintains parallel structure and effectively expresses the intended meaning, and ক. So does art accomplishes this most appropriately.