单项选择题 The highest frequency of a signal is ,sampling angular frequency is ,,  in order to avoid aliasing when sampling this signal, what pre-processing is required before sampling?(          )

单项选择题 空调系统的节能运行工况，在一年当中，新风量应为（   ）。 A、冬、夏季最小，过渡季最大 B、冬、夏季及过渡季都最小 C、冬、夏季最大，过渡季最小 D、冬、夏季及过渡季都最大

多项选择题 We regret to have to lodge a complaint against you about our loss arising from your late delivery of the coffee supplies we purchased under our Order No.OP7836.The word underlined can be substituted for by the following: A、file B、get in   C、make D、put in