"There's a story in the book" should NOT be marked wrong. It's literally the same thing. I reported the issue.
"The book has a story". This is also write.
It's also "right" not "write".
And yes, you're right. :)
story is singular why i need "a "
In English you pretty much always need an article like "a" or "the" for a singular item
You can't say "I watched film," you have to say, "I watched a film".
You can't say "there is story…" you have to say, "there is a story in the book".