最大的人工辐射源是（）
A.核能污染
B.医疗照射
C.天然辐射
D.核爆炸
E.氡放射
参考答案：B
腹部CT图像观察的窗参数，正确的是（）
A.肝胆窗宽200～400HU
B.肝胆窗宽100～200HU
C.肝胆窗宽150～300HU
D.肾上腺窗宽100～200HU
E.肾上腺窗位50～60HU
If the weather had been better, we could have had a picnic. But it ____ all day.
A．rains
B．rained
C．has rained
D．is raining
