Translation:One of the athletes is not running, but walking.
There is no plural in the Hungarian sentence at all. Literally read it is more like "The one athlete does not run, but walks." But the typical idiomatic English way to phrase that involves a plural construct, "One of the athletes..."
Thank you. Again "does not run but walks" was again rejected by the system. This issue is still not resolved although I, as well as other duolinguists, have reported it over and over..
We need to be patient, there is sooooo much to correct in the course. But I have seen much improvement already. So, please, just keep reporting the issues.
On "one of the athletes", you could translate it more closely as "a sportolók egyike". So you have your plural athletes. It is perfectly okay to say it like this, but the other way ("az egyik sportoló") is much more common.
Now it is a year later, and it still has not been corrected. I also am getting the feeling that work has stopped on the Hungarian duolingo. The same problems come up over and over again, I report over and over again, but nothing is happening. I used to get reports saying that my suggested version was good, and is being included. I no longer get those messages. While I appreciate everything that has been done. it is becoming increasingly frustrating.
"The one athlete is not running but walking" was marked incorrect. I am really getting irritated by these mistakes. They need to allow more variations