The number of six digits is () A. 40B. 60C. 80D. 10

The number of six digits is () A. 40B. 60C. 80D. 10

If the number of single digits is even, if 2 is in the single digit, then 1 is in the ten digit, and there are a22a22 = 4. If 2 is not in the single digit, there are A12 · A12 · A22 · A22 = 16. If the number of single digits is even, there are 4 + 16 = 20 six digits. Similarly, if the number of single digits is odd, there are 20 six digits that meet the conditions, and the number of such six digits is 40