Some europeans view immigrants as a threat because they
a) take employment away from "natives"
b) reconstruct cities
c) live in the country
d) increase the threat of terrorism
e) they dilute european culture
f) they create negative population growth

D) Increase the threat of terrorism

Explanation:

Lot of people in the European countries are worried about the immigrants and see them as threat. One of the main reasons for this is that with the bigger immigration the chances of terrorism are increasing. While the majority of the immigrants are not connected in any way with terrorists, there is small portion that is, and the big migration waves are used by the terrorist to infiltrate into the European countries. Once there, they start committing terrorist actions, resulting in injured or dead people, so the people get scared understandably. Unfortunately, the suspicion falls onto most of the immigrants after that, and that causes problems. In order for this to be solved, so that the natives feel safe, and the immigrants don't face discrimination, the governments should be much more careful as to who they let in their countries, and try to eliminate any possibility of terrorists being able to get in.