2、69
3、 1
4, if "nothing" is five.
B, C
The second question: (69)
36
19
10
five
2
33
17
nine
five
three
16
eight
four
2
The number of the next line is the difference between two adjacent numbers of the previous line (for example, 33=69-36), and the rule of the last line is 2 to the fifth power -n (n is the number of digits).