We were flying_______the clouds and saw the blue sky. [ ]
A. over
B. on
C. above
D. up
答案:C
弯制有缝钢管时,其纵向焊缝应放在距中性线()的地方。
能将X线直接转换成电子信号的材料是
A.碘化钠B.碘化铯C.非晶硒D.氟氯化钡·铕E.溴化钾