According to the article about Mt. Pinatubo's eruption , what caused thousands of roofs to collapse ? A. The eruption triggered an earthquake , which caused roofs to collapse .

B. The violent shaking of the eruption caused roofs to collapse .

C. The ash mixed with the typhoon's rain became too heavy for roofs to support .

D. The eruption spewed out large rocks , which landed on roofs and caused them to collapse .

How did northem leaders try to encourage americans to buy goods made in the united states rather than foreign imports? a high taxes on imports to increase the cost of imported goods b low taxes on imports to increase the cost of imported goods c. high taxes on imports to decrease the cost of imported goods d. low taxes on imports to decrease the cost of imported goods e high taxes on imports to decrease the cost of manufactured goods

Why might collective bargaining fail, causing a union to go on strike? a the union agrees with the boss about wages. b the boss compromises about work hours. c the factory goes out of business, causing the workers to lose their jobs. d the boss refuses to address dangerous working conditions in the factories.

Why do many scientists suppose the land bridge theory of migration?