We should try to solve the food safety. It is a serious _______ in our country.
A:subject
B:program
C:problem
D:opinion
下列哪项不是家鸽与飞行生活相适应的特点( )
山区常见的地质方面的自然灾害是____、____和____。
This is an art room.
某同学用显微镜观察玻片标本时,发现视野中有污点存在,移动玻片时污点不动,换上高倍物镜,污点仍存在,那么污点在
( )