According to this passage, what is the ultimate reason for the development of suburbanization

A．the social stress conditions as well as urban crowding
B．the transformation of compact cities into scattered metropolis
C．the development of electric traction lines
D．the emergence of Middle Class in cities

A．able to prey even when they are in deep dream sleep
B．more likely to experience dream sleep
C．incapable of preying when immobilized by dreamless sleep
D．good at preying on stupid animals