There are often 28 days in _______. [ ]
A. September
B. October
C. January
D. February
答案:D
使50%实验动物死亡的最低剂量为
A.致死剂量B.半数致死量C.绝对致死量D.最低致死量E.最大耐受量
显影液中若忘了添加促进剂按正常显影条件冲洗出的胶卷将()