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问题 选择题

Occasions are quite rare         the father has the time to spend a day with his kids．

A．when

B．which

C．why

D．that

答案

答案：A

单项选择题

We have already covered the topic of network addresses. The first  (1) in a block (in classes A, B, and C) defines the network address. In classes A, B, and C,if the hostid is all ls,the address is called a direct broadcast address. It is used by a(2) to send a packet to all hosts in a specific network. All hosts will accept a packet having this type of destination address. Note that this address can be used only as a (3) address in an IP packet. Note also that this special address also reduces the number of available hostid for each netid in classes A,B，and C． In classes A, B, and C, an address with all ls for the netid and hostid (32bits) define a (4) address in the current network.A host that wants to send a message to every other host can use this address as a destination address in an IP packet. However, a router will block a packet having this type of address to confine the broadcasting to the (5) network. Note that this address belongs to class E.

空白（1）处应选择（）

A.datagram

B.function

C.address

D.service
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单项选择题

硅酸盐玻璃中含有（）金属氧化物的耐水性最强。

A.二氧化锌

B.三氧化二铝

C.氧化镁

D.氧化钙
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