数学模型的描述方法之一是，当对象的数学模型是采用曲线或数据表格等来表示时，称为输入参数和输出参数模型。
参考答案：错
I saw Danny five boxes of frames and two rolls of film that day.[ ]
A. to buy
B. bought
C. are buying
D. buying
Look_______ the birds. They are lovely.
A．at
B．up
C．for
D．on
