家具实样是按家具的设计功能、尺寸、材料和工艺要求制作的真实的家具样品模型。( )

It is critical for your company to offer its products on the internet to increase its market share. The company has no previous experience in this area, but it believes that knowledge is needed rapidly. As you have shown an interest in the internet, you are asked to start planning for this project. What is the FIRST step to take as you begin planning

A．Identify the risk

B．Plan the scop

C．Establish a resource pla

D．Complete a cost and schedule estimat

下列不属于调查的是[ ]

A．统计我国人口的平均收入

B．统计全班同学的视力情况

C．显微镜下观察洋葱表皮细胞

D．调查一块农田中的生物种类

癌基因的确切定义是

A．Rous肉瘤病毒的核苷酸序列
B．一种RNA病毒的核苷酸序列
C．一种DNA病毒的核苷酸序列
D．哺乳类中与肿瘤发生相关的DNA序列
E．哺乳类中与细胞生长调控相关的 DNA序列

试比较倒牵伸与顺牵伸。

如图所示，一根不可伸长的细绳两端分别连接在框架上的A、B两点，细绳绕过光滑的滑轮，重物悬挂于滑轮下，处于静止状态．若缓慢移动细绳的两端，则绳中拉力大小变化的情况是（）

A.只将绳的左端移向A′点，拉力变大

B.只将绳的左端移向A′点，拉力不变

C.只将绳的右端移向B′点，拉力变小

D.只将绳的右端移向B′点，拉力变大