"Zij zijn normaal gesproken bruin."
Vertaling:They are normally brown.
Duolingo's vertaling is correct. "Normally" betekent "over het algemeen".
You don't say they are normally brown in English, you would say they are generally brown, or usually they are brown, it is only in French where they say, normalement bla bla bla and the Flemish who translate that into Dutch I think... Or am I missing something with what you're trying to say here ?
You certainly can say that something is normally... Sure you can use generally or usually, though in this case it aids learning to use a word that is closer to the Dutch normaal gesproken.
- "Bearded tits are normally brown and black...." - http://news.bbc.co.uk/2/hi/uk_news/england/lancashire/6189634.stm
- "The lights are normally blue,..." - https://www.theguardian.com/sustainable-business/2015/nov/06/renewable-energy-climate-change-land-art-generator-initiative
- "The colourful jumpsuits – which are normally orange – are a common sight in the USA." - https://www.telegraph.co.uk/news/worldnews/northamerica/usa/10985848/Michigan-jail-ditches-trendy-orange-prison-fatigues.html
- The ultra-softs, which are normally purple, have been transformed pink for this race as Formula 1 highlights Breast Cancer Awareness Month. - https://www.bbc.com/sport/live/formula1/40624879
- It is normally red. - https://www.bbc.com/education/guides/z8kkrwx/revision/6
I guess it depends on where and when you were educated ....
Had you quoted from Shakespeare or Mark Twain or an Oxford grammar book instead of from the press it may have been convincing. I would say that this silly English way of saying usually probably originated from Flemish or Dutch indigenous people living in the UK and then it unfortunately spread elsewhere but I'm only guessing ;-) And please, no more bearded tits ;-) Thanks for answering.
- Any of the longer keys on a keyboard instrument that are normally white. - https://en.oxforddictionaries.com/definition/us/natural
- ...and is normally yellow in color - http://www.oxfordreference.com/view/10.1093/oi/authority.20110803100321262
Perhaps you appreciate these better so.