Es gibt VS Es ist?
I just had a sentence in the German -> English tree where it said
"There is a tourist in the museum"
So I translated that as:
"Es gibt ein Tourist im Museum"
But "Es ist ein Tourist im Museum" was the right answer.
What's the difference?
"Es ist" or "Es sind" is used for situations are current, whereas "Es gibt" is used for general statements. For example:
Es sind viele Leute auf der Party (there are many people at the party (which is happening right now))
Es ist nur eine Blume in der Vase (there is only one flower in the vase right now)
Es gibt viele Probleme im Leben (there are many problems in life (in general))
Here is a video with more examples: https://www.youtube.com/watch?reload=9&v=8BMk2R5ePPA
If you typed 'ein Tourist' that's what's incorrect about your answer. 'Es gibt' takes the accusative, so it should have been 'einen Tourist'. If that's what happened then Duo just gave you a correct answer closest to your answer.
Why 'Es ist ein....' instead of 'Es gibt einen....'? Probably Duo scans the sentence left to right and changes the first thing that makes the sentence work. Both sentences mean the same thing.
Christian has written elsewhere that one does not use es gibt when referring to people or animals in their home. Weird.
That's just something you learn along with 'es gibt'. There are surprisingly few online references explaining this. Here's a link to a dictionary definition of 'geben'. https://en.langenscheidt.com/german-english/geben?term=geben&q_cat=%2Fgerman-english%2F
If you scroll down to the discussion on 'geben' as an impersonal verb you'll see that the examples take accusative.
I would explain it this way: 'geben' is a transitive verb, so it takes a direct object. To be grammatically correct, the thing that exists ('a tourist' in the example) is the direct object so it has to be in the accusative.