一个环形的外圆半径是R,内圆半径是r,它的面积是( )A.πR2﹣πr2 B.(2πR﹣2πr)2 C.2π(R﹣r)2
0.897化成百分数是( )A.0.897% B.89.7% C.8.97%
1.02化成百分数是( )A.102% B.1.02% C.10.2%
1.225化成百分数是 ( )
2.8里面有几个1%?( )A.2.8 B.28 C.280
1.9%化成小数是( )A.0.019 B.0.19 C.1.9