The Emergency Quota Act of 1921 was passed to severely restrict immigration from Eastern and Southern Europe. The threat of Communism came from there. Option C is correct.
The Emergency Quota Act was implemented primary as a reaction to the large influx of Jews fleeing persecution in Eastern Europe and thus successfully restricted their immigration and that of other "undesirables" into the United States. The Act marked in the long run the major turning-point in American immigration policy since it provided two new features to American immigration law: numerical limits on immigration and the use of a quota system for establishing those limits.