质心测算法可用于：（）。
A.人口预测
B.缓冲区分析
C.人口变迁分析
D.人口分布
参考答案：D
不应该计入人工工资单价的费用是( )。
A．劳动保险费
B．职工福利费
C．劳动保护费
D．工资性补贴
—David, there _______ a dictionary and some books on your desk. Please put them away.
—OK. Mum. I'll do it right away. [ ]
A. is
B. are
C. has
D. have
