The third number: 40+15 = 55 55 ÷ 3 =18 ...1.

The fourth number:1+40 = 4141÷ 3 =13 ... 2

The fifth number: 1+2=3 3÷3= 1, and the remainder is 0.

The sixth number: 2+0 = 22 ÷ 3 = 0...2.

Seventh number: 2+0 = 2 2÷ 3 = 0...2.

Eighth number: 2+2 = 4 4 ÷ 3 = 1... 1.

The ninth number: 1+2=3 3÷3= 1 The remainder is 0.

Tenth number:1+0 =11÷ 3 = 0 ...1

Eleventh number:1+0 =11÷ 3 = 0 ...1.

Twelfth number: 1+ 1 = 22 ÷ 3 = 0...2.

Thirteenth number: 1+2=3 3÷3= 1 remainder is 0.

It can be seen that starting from the fourth number, according to the rule of "2, 0, 2, 2, 1, 0, 1, 1", they are arranged in groups of eight.

Subtract the first three from the number 1999, and 1999-3= 1996 (pieces).

Just look for how many eights are there in 1996, how many are left, and count them again.

1996÷8=249……4

In "2,0,2,2, 1, 0, 1, 1", the fourth one is 2.

So the number 1999 is 2.

Write like this:

3: 40+ 15=55 55÷3= 18…… 1

4: 1+40=4 1 4 1÷3= 13……2

5: 1+2 = 3 3 ÷ 3 = 1 The remainder is 0.

6: 2+0=2 2÷3=0……2

7: 2+0=2 2÷3=0……2

8: 2+2=4 4÷3= 1…… 1

9: 1+2 = 3 3 ÷ 3 = 1 The remainder is 0.

10: 1+0= 1 1÷3=0…… 1

1 1: 1+0= 1 1÷3=0…… 1

12: 1+ 1=2 2÷3=0……2

13:1+2 = 3 3 ÷ 3 =1The remainder is 0.

Starting from the fourth number, every eight groups are arranged as "2, 0, 2, 2, 1, 0, 1, 1".

1999-3 =1996 (a)1996 ÷ 8 = 249 ...

In "2,0,2,2, 1, 0, 1, 1", the fourth one is 2.

A: The number 1999 is 2.