Read the following context and choose the best option to answer the question.
Context: The police officers ascended the steps and checked every passport individually . I was again surprised when I did n't get my passport stamped . Once you cross one border within Central America , a stamp is not necessary until you leave the region .
Question: Why did the police check each passport ?
Options: 
A. To find a lost child based on their ID
B. To help out the border control agents
C. To try to return a laptop that they found
D. To check for criminals entering the country


D