Question

Which countries does the North European Plain run through?
Belarus
Bulgaria
Croatia
Macedonia
Poland
Russia

Answer 1

You will have to do a little bit of research, here is a hint:

in the entry entitled North European Plain
"major reference (in European Plain (plain, Europe): Physiography)
...all of western and northern France, Belgium, The Netherlands, southern Scandinavia, northern Germany, and nearly all of Poland; from northern France and Belgium eastward it commonly is called the North European Plain. In the east the plain generally is called the East European, or Russian, Plain."

-brittanica

Answer 2

Nope. Check out this article.

http://en.wikipedia.org/wiki/North_European_Plain

Answer 3

Bryce -- what is the source of your quotation?