交互作用模型认为技术创新是由（）和市场共同作用引发的。
A.政府
B.技术
C.企业
D.高校
参考答案：B
I have _________ all my papers but I still can't find my notes. [ ]
A. looked through
B. looked for
C. looked after
D. looked out
()是指同一种商品中，不同档次之间的价格差额。
A．品种差价
B．规格差价
C．档次差价
D．式样差价
