One Reason Why Unauthorized Immigration Is Not Always Vigorously Addressed

One reason why unauthorized immigration is not always vigorously addressed by policy makers or enforcement agencies in destination countries is that:

A) employers and consumers in destination countries often find that they benefit from immigration.
B) it is simply not that big a problem because there are very few illegal immigrants.
C) only consumers stand to lose from illegal immigration, and they have little lobbying power.
D) the trend toward completely free international migration in most countries means that the problem will go away soon.