Original sentence: A hovercraft rides on an air cushion, gliding over muddy swamps, ice and snow.
Corrected sentence (recommended): A hovercraft rides on an air cushion, gliding over muddy swamps, ice, and snow.
Why this change? (Easy steps for a 7-year-old)
- When you list three things, we put commas between them. Here the three things are muddy swamps, ice, and snow.
- The comma before the word "and" (called the Oxford comma) is optional, but it makes the list clearer. That is why we added a comma after "ice."
Other simple way to say it: A hovercraft floats on a cushion of air and can glide over swamps, ice, and snow.
Both versions are correct; adding the comma before "and" makes the list clearer.