Detailed Instructions: In this task, you will be shown a passage. You need to write a fill-in-the-gap question based on your understanding of the events that might be inferred from the passage. Your question should be answerable based on the passage and only have one correct answer. Show the gap in your question with a _ .
Problem:(CNN)In January 2014, 22-year old Redouane Hagaoui left his home in the Belgian town of Verviers. He was due to travel to Morocco to see his grandparents, but never arrived. Instead, Hagaoui went to Istanbul, called his family from somewhere in Turkey, and then vanished into Syria. His family and friends were stunned. One friend told the local newspaper SudInfo: "He doesn't even speak Arabic very well." On Friday, the day after Belgian police killed two extremists during a raid in Verviers, a CNN crew met Hagaoui's mother and sister at her home, just a few hundred yards from the scene of the shoot-out. At the time, Belgian media were suggesting he may have returned to Verviers and been killed in the police raid.At least 250 individuals are believed to have left Belgium to wage jihad in Iraq and SyriaAnalyst Pieter Van Ostaeyen says would-be fighters help each other with travel advice through social mediaISIS has made it clear it plans to send fighters to Europe, once western forces are "defeated"
Solution:
Van Vlierden says that given their modest resources, the _ security services have been pioneers in tracking fighters.