About straight-ticket ticket voting and run-off primaries. How valid are criticisms?

In the diagram below dab and dac are adjacent angles

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.

At which boundary does subduction stop occurring, resulting in a mountain range?