输血后非溶血性发热反应的最常见原因是（）
A.输血后感染
B.输血导致凝集反应
C.过敏反应
D.血液中存在致热原
E.血型不合
参考答案：D
I have no choice, ____ you see, but only to wish that I____my daughter to that sort of man. [ ]
A. which; shouldn't marry
B. as; shouldn't have married
C. which; mustn't have married
D. as; hadn't married
如图所示，电源电动势E0=15V。内阻r0=1Ω，电阻R1=30Ω,R2=60Ω。间距d=0.2m的两平行金属板水平放置，板间分布有垂直于纸面向里、磁感应强度B=1T的匀强磁场。闭合开关S，板间电场视为匀强电场，将一带正电的小球以初速度v=0.1m/s沿两板间中线水平射入板间。设滑动变阻器接入电路的阻值为Rx，忽略空气对小球的作用，取g=10m/s2。
小题1:当Rx=29Ω时，电阻R2消耗的电功率是多大？
小题2:若小球进入板间做匀速圆周运动并与板相碰，碰时速度与初速度的夹角为600，则Rx是多少？
