.B correct answer! Thanks!
Responding to xenophobic concerns, Congress passed an emergency law restricting immigration in 1921. Among other provisions, the Act established a quota (a proportional share of a total) for nationalities on the basis of their numbers in the U.S. in 1910.
The missing detail is: a quota.
Answer:
Paleolithic humans originated in one continent and then spread to many parts of the world
Explanation:
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