Respuesta :
Parallelism is one of the most important elements to be considered in constructing a sentence. In addition to that, parallelism is commonly defined to be useful in adding symmetry to a certain context. Therefore, the answer would be the third choice "plays that are tragic."
The answer to your question would be that to create a parallel structure in the sentence, the phrase that would replace the words "when the plays are tragic" best is the following one: Plays that are tragic.
Parallel structure, also known as parallelism, is the repetition of a grammatical construction within in a sentence. In this case, the construction repetead is the whole NP (the noun head and its modifiers: plays that are funny and plays that are tragic)