What do people tend to believe other's life is when they are in a big city

A．modern dams are all made of concrete
B．Romans once built many great dams
C．there was too much water in Iraq in the past
D．modern dams are better than early dams

A．a dam will be built across the river
B．a dam will store water for dry seasons
C．in wet seasons a dam will prevent the flooding of the land
D．houses and fields will be covered with water