中学生的大拇指指甲面积约为( )
A:1 mm2
B:1 cm2
C:1 dm2
D:1 m2
—The land in the southwest of China is in great need of .—Yes, it hasn't rained for a long time there.
下列结论:①4a>3a;②4+a>3+a;③4-a>3-a中,正确的是( )