16.
如图,一块长为a,宽为b的长方形草坪,上下开辟的花园,都是由等半径的两个四分之一圆和一个半圆组成,那么中间草坪的面积是( )
0 288839 288847 288853 288857 288863 288865 288869 288875 288877 288883 288889 288893 288895 288899 288905 288907 288913 288917 288919 288923 288925 288929 288931 288933 288934 288935 288937 288938 288939 288941 288943 288947 288949 288953 288955 288959 288965 288967 288973 288977 288979 288983 288989 288995 288997 289003 289007 289009 289015 289019 289025 289033 366461
| A. | ab-πb2 | B. | ab-$\frac{π}{2}$b2 | C. | ab-$\frac{π}{4}$b2 | D. | ab-$\frac{π}{8}$b2 |