In the last paragraph, the word "escalate" means ______.
A) decrease C) go down
B) increase D) decline

A．conclusions reached by the U.N. study
B．Rafael M. Salas's personal opinions about the future
C．the rate of population growth
D．a flood of migration from rural areas

A．people should be encouraged to live in the urban centers
B．government should encourage people to live in the rural areas
C．people have more advantages in the countryside
D．living in the countryside is better than in the big cities