移项，3x≤9，
解得x≤3．
故选C．
With the development of the Internet, _____ communication will be done by regular mail. [ ]
A. more
B. less
C. much
D. little
逆温的强度指( )。
A．逆温的持续时间 B．逆温的出现次数C．每升高100m气温的增加 D．每升高100m逆温顶、底标高差
