图示结构在水平杆AB的B端作用一铅直向下的力P,各杆自重不计,铰支座A的反力R的作用线应该是( )。

A:R沿水平线 B:R沿铅垂线 C:R沿A,D连线 D:R与水平杆AB间的夹角为300

轴AB与铅垂线成α角。悬臂OD垂直地固定在轴上，长为a，并与铅垂面AzB成θ角。若在D点作用铅垂向下的力P，此力对AB轴的矩为( )。

A:M(P)=Pasinαcosθ B:M(P)=Pasinαsinθ C:M=Pacosαsinθ D:M(P)=Pacosαcosθ

如图12-5所示在一混凝土厂房内用厂形钢制刚架搭建一个不直接承受动力荷载的工作平台。横梁上承受均布荷载设计值q=45kN／m，柱顶有一集中荷载设计值P=93kN。钢材用Q235-B。刚架横梁的一端与混凝土柱铰接（刚架可不考虑侧移）；其结构的计算简图,梁柱的截面特性以及弯矩计算结果见图12-5所示。已知柱间有垂直支撑，A,B点可作为AB柱的侧向支承点。

柱AB在刚架平面内的计算长度(m)，与下列何项数值最为接近？

A:4.20 B:3.50 C:3.05 D:2.94

如图所示机构中，AB和CD两杆在E点用铰链相连。它们相互垂直，水平杆AH的A端与AB杆铰接，而其中点D与CD杆的D端为光滑接触。滑块B置于水平光滑面上，各构件的重量不计。当机构在图示铅直力P和水平力Q作用下处于平衡时，P、Q两力的大小之间的关系是（）。  

A:Q=3/2P B:Q=1/2P C:Q=P D:Q=2P

轴AB与铅垂线成α角。悬臂OD垂直地固定在轴上，长为a，并与铅垂面AZB成θ角。若在D点作用铅垂向下的力P，此力对AB轴的矩为（）。

A:M_AB(P)=Pasinαcosθ B:M_AB(P)=Pasinαsinθ C:M_AB(P)=Pacosαsinθ D:M_AB(P)=Pacosαcosθ

杆AF、BE、EF相互铰接并支承，如图所示。今在AF杆上作用一力偶（P、P′），若不计各杆自重，则A支座反力的作用线应：（）。

A:过A点平行力P B:过A点平行BG连线 C:沿AG直线 D:沿AH直线

如图所示，AB和BC是由同种材料制成的长度相同、横截面积不同的两段导体，将它们串联后连入电路中，这两段导体两端的电压及通过它们的电流的大小关系正确的是（）。

A:U_AB＞U_BC I_AB=I_BC B:U_AB＜U_BC I_AB=I_BC C:U_AB＞U_BC I_AB＜I_BC D:U_AB=U_BC I_AB＜I_BC

点C是线段AB上的一个动点，AB=1，分别以AC和CB为一边作正方形，用S表示这两个正方形的面积之和，下列判断正确的是（）。

A:当C是AB的中点时，S最小 B:当C是AB的中点时，S最大 C:当C为AB的三等分点时，S最小 D:当C为AB的三等分点时，S最大

Passage Four
You have been badly injured in a car accident. It is necessary to give you a blood transfusion because you lost a great deal of blood in the accident. However, special care must be taken in selecting new blood for you. If the blood is too different from your own, the transfusion could kill you.
There are four basic types of blood; A, B, AB and O. A simple test can indicate a person’s blood type. Everybody is born with one of these four types of blood. Blood type, like hair color and height, is inherited from parents.
Because of substances contained in each type, the four groups must be transfused carefully. Basically, A and B cannot be mixed. A and B cannot receive AB, but AB may receive A or B.O can give to any other group, hence it is often called the universal donor. For the opposite reason, AB sometimes called the universal recipient. However, because so many reactions can occur in transfusions, patients usually receive only salt or plasma until their blood can be matched as exactly as possible in the blood bank of a hospital. In this way, it is possible to avoid any bad reactions to the transfusion.
There is a relationship between your blood type and your nationality. Among Europeans and people of European ancestry, about 42 percent have type A while 45 percent have type O. The rarest is type AB. Other races have different percentages. For example, some American Indian groups have nearly 100 percent type O.

A:A B:B C:AB D:O

已知事件A与B为相互独立事件，则P(AB)=( )

A:P(A)+P(B) B:P(A)-P(B) C:P(A)+P(B)-P(A)P(B) D:P(A)P(B)