Question

Which sentence contains a hyphen error? About one third of my friends have pet dogs. It is a well known fact that the earth revolves around the sun. We used one-half cup of chopped onions in the recipe. It will be chilly later, so bring your blue-green sweater.

Answer 1

I'm just confirming that this is the correct answer I just took the test

Answer 2

I believe it would be About one third of my friends have pet dogs. 

Fractions should be hyphenated.