Question

correct the text by inserting two commas. (note: in this skill, serial commas are not optional)
the united states is not the only country with a red white and blue flag: the flags of over thirty other nations use the same colors.

Explanation:

1. Add a comma after "red" to separate the coordinate adjectives/color items in the list.
2. Add a comma after "white" (even though the note says serial commas are optional, this is the standard way to insert the second required comma to properly separate the three color terms in the phrase "red, white, and blue").

Answer:

The United States is not the only country with a red, white, and blue flag; the flags of over thirty other nations use the same colors.