1, the first seven digits are removed from the hundredth digit, and the last two digits correspond to 0 and 6, so only one of the two spaces can be selected. The last two represent 6 in two cases: 6 and 9.

2, then 7c2 means that the remaining two squares are randomly selected from seven, 3! It means that three numbers are randomly arranged, and the last one means that 6 has two situations: 6 and 9.

3. That 7c2 means that the remaining two squares are randomly selected from seven, and the selected numbers are placed in two situations. The last 2 indicates that the last two numbers are randomly arranged.

4. That 7c2 means that the remaining two squares are randomly selected from seven, and then three! It means that three numbers are arranged randomly.