Please help! Will mark brainlist

What evidence does the writer give to support his argument about coral reefs? a) he speaks of the activities of coral polyps. b) he describes the composition of the great barrier reef. c) he emphasizes the ways in which coral reefs are fragile. d) he points out the ways that scientists do research on the reefs.

Given: circle a externally tangent to circle b. how many possible common tangents to circles a and b can exist? 2 3 4

Why is the study of demography important to geographers