A compare-and-contrast essay is a style of essay that points out the similarities and differences between two or more subjects. It's ideal for showing what separates and unites related things or concepts, particularly if the subjects are often confused for each other or unjustly lumped together.
The type of sentence is a question, is that what you're looking for?
Answer:
Commas are used in a series to describe something without saying 'and'
