搜题请搜索小程序“爱下问搜题”
问题 选择题

化学是研究物质的组成、结构、性质及其变化规律的科学．下列选项中属于物质的化学性质的是（　　）

A．挥发性

B．可燃性

C．熔点

D．密度

答案

A、挥发性不需要通过化学变化表现出来，属于物质的物理性质；

B、可燃性需要通过化学变化表现出来，属于物质的化学性质；

C、熔点不需要通过化学变化表现出来，属于物质的物理性质；

D、密度不需要通过化学变化表现出来，属于物质的物理性质．

故选B．

单项选择题

上颌切牙有

A．唇舌面的外形高点在中1/3
B．中切牙切缘与近中切角近似直角
C．上颌侧切牙近中切角似锐角
D．上颌侧切牙舌窝较浅
E．较常发生变异
查看答案
单项选择题

The network layer provides services to the transport layer. It can be based on either___20___. In both cases, its main job is ___21___ packets from the source to the destination.

In network layer, subnets can easily become congested, ncreasing the delay and ___22___ for packets. Network designers attempt to avoid congestion by proper design. Techniques include___23___ policy, caching, flow control, and more.

The next step beyond just dealing with congestion is to actually try to achieve a promised quality of service. The methods that can be used for this include buffering at the client, traffic shaping, resource___24___, and admission control. Approaches that have been designed for good quality of service include integrated services (including RSVP), differentiated services, and MPLS.

23（）

A. abandonment

B. retransmission

C. checksum

D. synchronism
查看答案