搜题请搜索小程序“爱下问搜题”
问题 单项选择题

传输层主要任务是向用户提供可靠的 ______。

A．虚电路服务

B．点到点服务

C．分组交换服务

D．端到端服务

答案

参考答案：D

解析：[知识点] ISO/OSI参考模型[评析] 根据分而治之的原则，ISO将整个通信功能划分为7个层次：物理层、数据链路层、网络层、传输层、会话层、表示层、应用层。其中传输层的主要任务是向用户提供可靠的端到端服务，透明地传送报文。它向高层屏蔽了下层数据通信的细节，因而是计算机通信体系结构中最关键的一层。

判断题

在特别潮湿和金属容器内工作，手灯工作电压不得超过36V。()
查看答案
单项选择题

B


It keeps your insides from falling out. It helps you warm up when you are cold, and it can cool you off when you are hot. It lets you feel things by touch.
What is this Your skin, of course! What does your skin ask for in return for all the wonderful things it does Just a little care! So let’s learn how to take good care of our skin.
Like the heart and stomach, your skin is an organ(器官). In fact, it is the largest organ in your body. Unless there’s a problem, you may not think about your skin very much. But skin has an important job to do.
Your skin is protecting you. Your skin keeps you from getting sick. When you take care of your skin, you are helping your skin do its job. Taking care of your skin today will help you have no problems in the future.
Clean skin is happy skin! One simple way to take care of your skin is to keep it clean. Keeping your hands clean is very important. When washing your hands, use warm water. Wet your hands, and then use soap. You should wash your hands carefully everywhere.
You’ll also want to use warm water, but not too hot, when you take a bath. Use soap to clean your body. Don’t forget under your arms and behind your ears! Your face needs attention, too. It’s a good idea to wash your face once or twice a day with warm water.

Why does the writer think we should try to take care of our skin today ( )

A．To help us warm up when we are cold.

B．In order to keep our insides from falling out.

C．In order to help us have no problems in the future.

D．To let us feel things by touc
查看答案