The speaker mentioned all of the following as effects of mass transportation on cities EXCEPT a. Growth in city area. b. Separation of commercial and residential areas. c. Changes in life in the inner city. d. Increased standards of living.

空气、水、金属固体的热导率(导热系数)分别为λl、λ2和λ3，其顺序为λl<λ2<λ3。