Tigers and bears are very dangerous. That's () they have to stay in cages in the zoo.
A. why
B. where
C. how
D. what
Masson Fontana黑色素银浸染色的正确结果是
A. 黑色素呈黑色
B. 黑色素呈暗绿色
C. 嗜银细胞颗粒呈棕色D.细胞核呈蓝色
D. 胶原纤维呈紫色
If only I ()how to operate a computer as you do.
A. had known
B. would know
C. should know
D. knew
Molish反应需要的试剂为
A. 邻苯二甲酸-苯胺
B. α-萘酚-浓H2SO4
C. Fe3+/并冰醋酸-浓H2S04
D. HCl-羟胺
E. 醋酐一浓硫酸试剂