Which technique of writing does the author use in portraying
Dr. Hood in this passage?

indirect characterization

direct characterization

internal monologue

show, don't tell

The Absence of Mr Glass
by G. K. Chesterton (excerpt)

Dr Hood paced the length of his string of apartments, bounded—as the boys' geographies say—on the east by the North Sea and on the west by the serried ranks of his sociological and criminologist library. He was clad in an artist's velvet, but with none of an artist's negligence; his hair was heavily shot with grey, but growing thick and healthy; his face was lean, but sanguine and expectant. Everything about him and his room indicated something at once rigid and restless, like that great northern sea by which (on pure principles of hygiene) he had built his home.