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问题 填空题

二次函数y=ax2+bx+c的图象在x轴上方的条件是______．

答案

欲保证x取一切实数时，函数值y恒为正，则必须保证抛物线开口向上，且与x轴无交点；

则a＞0且△=b2-4ac＜0．

单项选择题

最常见的贫血类型？（）

A.巨幼红细胞性贫血；

B.再生障碍性贫血；

C.缺铁性贫血；

D.溶血性贫血；

E.慢性炎症性贫血。
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单项选择题

Most IP layer-based proxy mechanisms, such as network address translation (NAT), only support uni-directional proxy, from the internal network to external network (the Internet). The proxy establishes the communication channel by (66) IP addresses. The IP addresses must be (67) . These proxy mechanisms prevent applications that must establish return data channels from establishing their data channels, such as, multimedia applications. IP layer-based proxy mechanisms need additional software (68) for each application that uses (69) channels. SOCKS identifies communication targets through domain names, overcoming the restriction of using private IP addresses. SOCKS can use domain names to establish communication between separate LANs, with (70) IP addresses.

A．routable

B．locatable

C．path-selected

D．road-defined
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