Q20. Answer: 4. Sentences 1, 2, 3, and 5 form a coherent paragraph about early-twentieth-century museum theory: the conviction that arrangement could substitute for explicit theory (1, 2), the practical consequence (3), and the underlying theory of viewing (5). Sentence 4 is on the same broad theme (museum design) but shifts to modern interactive screens and visitor customisation, which belongs to a different stage of argument. The oddness is structural, not topical.