Which word in the sentence, if any, should be followed by a colon? Countries in Eastern Europe include Bulgaria, Poland, Belarus, and Ukraine.

a. include

b. Countries

c. There is no error in colon usage.

d. Eastern

If you really really absolutely want to include a colon in this sentence (but you don't have to) then it should be after the word "include" - option a. : Countries in Eastern Europe include: Bulgaria, Poland, Belarus, and Ukraine.

But I think that it is better without a colon, and option c. is better!