辨别表证最主要的症状是（）
A.发热
B.恶寒
C.头痛
D.脉浮
E.舌苔薄白
参考答案：B
Mr. Black was so____ to his research that he seldom cared about what happened around him.
A．devoted
B．concerned
C．absorbed
D．used
用10Ci的铱192放射源在野外对距其1m处厚20mm的钢进行透照拍片，已知该射源的电离常数为0.6rhm/Ci，对钢的半值层为10mm，为了获得2.0黑度的底片需要曝光（）。
A.10min
B.20min
C.30min
D.40min
