Pick up the wrong answer

[finix33]

Passports (are legal)1 documents (issued by)2 government to give their bearers an authorization to (cross nation)3 borders and (seek protection)3 in an emergency.

I couldn't work out why did the book put (3):cross nation as the wrong answer.

Never mind, I found it :-D, sorry for being hurried. Nation should have been national in order to make the sentence correct.

 

[Tarheel]

A passport is to help get you there, but it also is for ensuring that you can come back.

http://dictionary.reference.com/browse/passport?s=t