Question

which type of geographic tool would best help show where immigrants to the us moved over time?
a us map showing population distribution
a timeline of changes in immigration policies
a bar graph showing total immigration numbers
a world map showing immigration routes

Explanation:

A world map showing immigration routes would display the paths immigrants took to the US over time, fulfilling the requirement of showing movement. A population - distribution map doesn't show movement, a timeline of policies is about policy changes not movement, and a bar graph of total numbers doesn't show movement paths.

Answer:

a world map showing immigration routes