Why Was a Quota of 20,000 Immigrants from Mexico, as Set

Why was a quota of 20,000 immigrants from Mexico, as set by the Immigration and Nationality Act, so unrealistic?

A) Because Chinese laborers had largely replaced Mexican laborers in the United States, so such a large quota was unnecessary
B) Because at the time, anti-Mexican sentiment was so intense that Americans would never have stood for such a large quota
C) Because agricultural initiatives were on the rise in Mexico, creating an incentive for Mexican laborers to stay in Mexico for work
D) Because the need for Mexican labor to sustain economic growth in the United States was so much greater than what the quota allowed for