( )是市场机制的核心。
A．竞争机制
B．供求机制
C．价格机制
D．要素机制
参考答案：C
已知f（2x+1）=x2-2x，则f（2）=______．
It is five years since we began to enjoy a _______ spring holiday each year. [ ]
A. ten-day
B. ten day
C. ten day's
D. ten-days
