Which sentence uses a dash to set off a parenthetical aside?

• A. The experiment—despite its flaws—proceeded.
• B. The experiment— despite its flaws—proceeded.
• C. The experiment, despite its flaws—proceeded.
• D. The experiment—despite its flaws proceeded.

Answer: (A)

Using em dashes to set off a parenthetical aside is the idea here. The phrase inside—the aside “despite its flaws”—acts like a quick interruption or extra comment that isn’t essential to the main point, which is that the experiment proceeded. The clean, standard way is to sandwich that aside with dashes on both sides and to have no space immediately next to the dashes, so the sentence reads as a seamless main clause with a sharp, brief interruption: The experiment—despite its flaws—proceeded.

The other forms break that pattern. Putting a space after the opening dash breaks the conventional tight connection between the dash and the following word, making it look inconsistent. Mixing a comma with the dash inside also muddles the interruption, and leaving out the closing dash means the aside isn’t properly closed, leaving the sentence ungrammatical.