I hope that the choir in the front row sits down soon; I cannot see the concert because ___ blocking my view.

The correct choice is "their" because it functions as a possessive pronoun, indicating ownership of the obstruction that is blocking the speaker's view. In this case, "their" refers to the choir, which is a collective noun made up of multiple individuals. Therefore, the correct sentence reads: "I cannot see the concert because their blocking my view," implying that the choir members are the ones who are causing the obstruction.

Using "it is," "they are," or "its" does not properly convey that the choir—made up of many singers—is collectively responsible for blocking the view. "It is" suggests a singular subject that doesn't fit with the plural nature of the choir. "They are" would require a rephrasing of the sentence to work, while "its" implies singular possession, which does not align with the collective noun in this context.