凝汽器满水、抽气工作失常和（），以及真空系统严密性突然遭到破坏等情况会引起凝汽器中真

（选做题，选修3-5）

在光滑的水平地面上静止着一质量为M=0.4 kg的薄木板，一个质量为m= 0.2 kg的木块（可视为质点）以v₀=4 m/s的速度，从木板左端滑上，一段时间后，又从木板上滑下（不计木块滑下时机械能损失），两物体仍沿直线继续向前运动，从木块与木板刚刚分离开始计时，经时间t=3.0 s，两物体之间的距离增加了s=3 m，已知木块与木板之间的动摩擦因数μ=0.4，求薄木板的长度。

帕金森病康复治疗不包括（）。

A.松弛训练

B.姿势训练

C.步态训练

D.面肌训练

E.感知觉训练

客户关系的退化期是客户关系的逆转阶段，关系退化（）

A.可能发生在考察期

B.可能发生在形成期

C.可能发生在稳定期

D.只能发生在稳定期之后

We had guests last night who have not stayed in a B&B hotel ago. They did not want breakfast because that they were going out early in the morning. They came back lately and had some tea. I came into the living room and saw one of them just go through the kitchen door but turn on the light. He was looking for a glass the cupboard. He had no ideas that the kitchen was not for guests. I just smiled to me and thought, "What can I do We are guests after all. \

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少先队"手拉手"互助活动以互助互学、互献爱心为基本内容，以"四个一"为基本活动形式。"四个一"是指交一个朋友、写一封交友信、寄一本书和（）。

A.出一次国

B.看一次朋友

C.捐一次钱