Which sentence correctly uses a dash? 

1. She bought three items – apples, bananas, and oranges
2. She bought three items—apples, bananas, and oranges
3. She bought three items, apples, bananas, and oranges
4. She bought three items: apples, bananas, and oranges

Em dashes (—) introduce dramatic pauses or lists instead of colons for informal emphasis (MLA 2.2.6). Option a uses an en dash (–), which indicates ranges (e.g., 1990–2000). No spaces around em dashes. Overuse weakens writing impact.