已知f(x)=ax(a>0,且a≠1)在[1,2]上的最大值和最小值之和为12,则a的值为( )
A:3
B:4
C:﹣4
D:﹣4或3
香港和澳门都比较发达的经济部门是( )
When you want to learn a language, you should learn from the ________ words.