2. Six ones and 1 ten is ().
17 has () ten bits and () bits.
There are () tens in 4.20.
5. 12 The first number is (), and the last number is ().
6. The two numbers adjacent to 19 are () and ().
7. Arrange the following figures in descending order. 15, 7, 1 1, 17, 2, 0, 18, 20
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