17.用78.5米长的篱笆围成一个菜地,围成( )形状面积最大.
| A. | 长方形 | B. | 圆 | C. | 正方形 | D. | 梯形 |
15.把 $\frac{2}{9}$的分子扩大2倍,要使这个分数大小不变,分母应该( )
0 134767 134775 134781 134785 134791 134793 134797 134803 134805 134811 134817 134821 134823 134827 134833 134835 134841 134845 134847 134851 134853 134857 134859 134861 134862 134863 134865 134866 134867 134869 134871 134875 134877 134881 134883 134887 134893 134895 134901 134905 134907 134911 134917 134923 134925 134931 134935 134937 134943 134947 134953 134961 199269
| A. | 增加2 | B. | 增加9 | C. | 减少2 | D. | 减少9 |