7 8 9 78 789 789 987 78987 778899 998877 779988 879 987 78998 78998 87998 77889 99887 78987 87987 78987 77987 77899 99877 7789 9987 7789 9987 8879 8897 88779 99887 7788998 7788997 7788999 998877 778899 777888999 999888777

混合练习：78987 98798 88789 87787 89878 98888 78978 98798 89789 78798 79879 79888 79777 89879 87958 98798 79878