What is the passage mainly about?
A.Ozone's usefulness.
B.Ozone's harmfulness.
C.Ozone's protection.
D.Ozone.
"Managed trade" in the last Sentence probably means ______.
A.market management
B.trade protectionism
C.trade concession
D.market priority
A.They are like grown-up children.
B.They feel very insecure.
C.They long for being protected.
D.They feel extremely lonely.
A great deal has been done to remedy the situation.
A. maintain
B. improve
C. assess
D. protect