Items in the catergory of goods are difficult to trace even when their identification numbers are present.

a)smuggled
b)imported
c)perishable
d)fungible

I believe the correct answer from the choices listed above is option A. Items in the category of smuggled goods are difficult to trace even when their identification numbers are present. These goods are  imported or exported secretly, in violation of the law. It cannot be tracked freely since they are done secretly. Hope this answers the question.