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问题 计算题

某太阳能热水器内盛有20℃的水50kg，在阳光照射下水温升高到 60℃。试计算在此过程中这些水吸收了多少热量。[c水=4.2× 103J/(kg·℃)]

答案

解：Q吸=cm(t末－t初)

             =4.2×103J/（kg·℃）×50kg×（60℃－20℃） 

             =8.4×106J。

多项选择题

某工程网络图如下，监理工程师在第4天末检查进度，则（）。

A．工作D比原计划拖后1天，且影响工期1天

B．工作D比原计划拖后1天，但由于有2天时差不会影响工期

C．工作C比原计划拖后2天

D．工作C比原计划超前1天

E．工作E已顺利完成
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单项选择题

Bluetooth is a universal radio interface in the (1) frequency hand that enables portable electronic devices to connect and communicate wirelessly via short-range, ad hoc networks. Each unit can simultaneously communicate with up to (2) other units per piconet. Moreover, each unit can simultaneously (3) to several piconets. Eliminates the need for wires, cables and connectors for and between cordless or mobile phones, modems, headsets, PDAs, Computers, printers, projectors, local area networks, and so on, and paves the way for new and completely different devices and applications. Technology Characteristics (4) symbol rate exploits maximum available (5) bandwidth。

2（）

A．server

B．firewall

C．clinet

D．router
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