万里长城是中 * * 古老文化的丰碑和智慧结晶，象征着中 * * 的血脉相承和民族精神。

目前已明确的肝炎病毒有5种，分为甲、乙、丙、丁、戊5种型别，引起的病毒性肝炎都具有传染性较强、传播途径复杂、发病率高的特点。其中甲型和戊型肝炎病毒的传播途径及引起的临床症状相似。

孕妇感染后病死率高的病毒是（）

A.HAV

B.HBV

C.HCV

D.HDV

E.HEV

如果一个竞争企业的生产技术为规模报酬不变，那么在长期内它能实现的最大利润为( )。

A．无穷大

B．零

C．不确定

D．以上答案都不对

教育只有正向功能，没有负向功能。

In (66) the strength of the carrier signal is varied to represent binary 1 or 0. (67) is a system that can map a name to an address and conversely an address to al name. (68) is a three-way handshaking authentication protocol that it’s packets are encapsulated in the point-to-point protocol. (69) is an approach that enables an ATM switch to behave like a LAN switch. (70) is an guided media which is made of glass or plastic and transmits signals in the form of light.

A．ASK

B．PSK

C．FSK

D．FDM

某750m³高炉日产生铁2000t，焦炭消耗700t，煤粉消耗320t。计算高炉的有效容积利用系数、焦比、煤比、综合冶炼强度。