关于各种非空线索二叉树中空指针的个数有如下说法：  

①任一非空先序线索二叉树有2个空指针。  

②任一非空中序线索二叉树有2个空指针。 

③任一非空后序线索二叉树有2个空指针。

其中说法准确的个数是(5)。

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  Remote administration types are an example of one kind of(71)malicious software, the Trojan horse, or more simply Trojan. The purpose of these programs isn't replication,(72)to penetrate and control. That masquerade as one thing when in fact they are something else, usually something destructive. There are a number of kinds of Trojans, including spybots, (73) report on the Web sites a computer user visits, and keybots or keyloggers, which record and report the user's keystrokes in order to discover passwords and other confidential information.

 RATS attempt to give a remote intruder administrative control of an infected computer. They work as(74)pairs. The server resides on the infected machine, while the client resides elsewhere, across the network, where it's available to a remote intruder. Using standard TCP/IP or UDP protocols, the client sends instructions to the server. The server does(75) it's told to do on the infected computer.

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现需要一个32M×8规格的存储器，现只有规格为1M×8的存储器芯片，则需要(49)个这样的存储器芯片。存储芯片的地址长度需要(50)位，主存储器的地址长度需要(51)位。

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