单项选择题We learn from the first paragraph that （）

A．dead leaves and tree debris make the same sound
B．trees that are dying usually give out a soft moan
C．organic debris echoes the sounds in a rain forest
D．the sound of a forest signifies its health condition

单项选择题Why do consumers, businesses and investors retreat and panic in times of depression（）

A．They suffer great losses in stocks, property and other assets.
B．They find the self-correcting mechanisms dysfunctioning.
C．They are afraid the normal social order will be paralyzed.
D．They don’t know what is going to happen in the future.