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问题 选择题

如图所示，质量为的物体在沿斜面向上的拉力F作用下沿斜面匀速下滑，已知斜面体的质量为M，并在此过程中斜面体保持静止，则地面对斜面体

A．摩擦力为零

B．有水平向左的摩擦力

C．支持力为

D．支持力小于

答案

BD

可以单独对两个物体进行受力分析，稍微复杂点，但不难；也可以对整体进行受力分析，如下图：

整体合外力为零

可以得出结论

单项选择题

The purpose of the requirements definition phase is to produce a clear, complete, consistent, and testable (16) of the technical requirements for the software product.
During the requirements definition phase, the requirements definition team uses an iterative process to expand a broad statement of the system requirements into a complete and detailed specification of each function that the software must perform and each _( 17) that it must meet. The starting point is usually a set of high level requirements from the (18) that describe the project or problem.
In either case, the requirements definition team formulates an overall concept for the system and then defines (19) showing how the system will be operated publishes the system and operations concept document and conducts a system concept review (SCR).
Following the SCR, the team derives (20) requirements for the system from the high level requirements and the system and operations concept. Using structured or object-oriented analysis, the team specifies the software functions and algorithms needed to satisfy each detailed requirement.

A．rules

B．principles

C．scenarios

D．scenes
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单项选择题 A1/A2型题

进行回收实验的样品浓度最好达到（）

A.病理标本的最高浓度值

B.病理标本的最低浓度值

C.参考值范围内的浓度值

D.医学决定水平的浓度值

E.参考范围的上限浓度值
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