Experts disagree as to why crime rates have continued to fall. Some say the U.S. _______ economy has made crime less attractive.

A．they feel it is a shame to let other people know
B．they don't know who they should turn to for help
C．professional help is too expensive
D．professional help is of no use

A．The United States has already established a public health system aiming at treating mental health emergencies.
B．The United States are better equipped than most countries in handling mental problems.
C．The United States was attacked by the terrorist.
D．Many American people now suffer from mental problems after the terrorist's attack.