Final answer:
Option A. Brackets are used to enclose additional, nonessential information within a sentence, effectively setting it apart without interrupting the sentence flow.
Step-by-step explanation:
The content that the writer sets apart without interrupting the flow of the sentence can be enclosed using brackets. Brackets are used to insert additional information into a sentence without detracting from the main message. They help by providing clarifying details or secondary information, and their use places less emphasis on the enclosed content compared to commas or dashes which could be used for similar purposes.
For example, in the sentence 'My sister, an excellent pianist (she has won several local competitions), is practicing for her next recital,' the detail about the sister being an award-winning pianist is placed in parentheses to provide additional information without interrupting the main point of the sentence.