Answer:
C. While foreign migrant workers are forced to leave the United States after a period of time, migrant workers from within the United States are able to stay and work indefinitely.
Explanation:
The author was trying to let us know that, due to the type of visa which the migrant workers have, they have no choice than to leave the US after the expiring of the validity while on the otherhand, the migrant workers from within US never had such issue.
Imagination, without any knowledge of the impossible you test the boundaries and redefine it. Logic is linear and does not question beyond already known concepts, although it may aid in current, defined situations- imagination is able to aid in all!