その男の子たちは一つのリンゴ食べます。I don't understand why my sentence translation was wrong. I used the katakana spelling for apple which should be correct.
「りんご」,「リンゴ」and 「林檎」should be all correct. But unfortunately, Japanese-English course is now beta version, so correct answers are often judged to be incorrect.
I think your sentence is lacking of "を" between りんご and 食べます。
You just might be right! lol