根据图示参考方向列出的方程，正确的是（）
A.U=E-IR
B.U=E+IR
C.U=-E+IR
D.U=-E-IR
参考答案：B
The poor boy seems _____ the news that his father died in the car accident for there is no sign of sorrow on his face.
A．not to be known
B．not to have received
C．to have not received
D．not to know
CT的膝关节扫描可见内外两侧的半月板，其密度均匀，CT值在
A．10～20HUB．30～40HUC．50～60HUD．70～90HUE．100～110HU
