20．通过估算．1×9.9的积与（ ）÷9.9的商最接近．
| A． | 10 | B． | 100 | C． | 1000 |
13．填空．
0 156837 156845 156851 156855 156861 156863 156867 156873 156875 156881 156887 156891 156893 156897 156903 156905 156911 156915 156917 156921 156923 156927 156929 156931 156932 156933 156935 156936 156937 156939 156941 156945 156947 156951 156953 156957 156963 156965 156971 156975 156977 156981 156987 156993 156995 157001 157005 157007 157013 157017 157023 157031 199269
| $\frac{1}{2}$+$\frac{1}{4}$=$\frac{3}{4}$ | 0.7+1.1=1.8 | 0.9-0.3=0.6 |
| $\frac{5}{8}$-$\frac{1}{2}$=$\frac{1}{8}$ | 7.8-0.8=7 | 1-$\frac{4}{5}$=$\frac{1}{5}$ |