12. Fill in the nine positions with 1 and 9, so that the sum of the numbers in the five rings is a sequence of consecutive natural numbers. Find the possible value of the total sum of the numbers in the open rings. $\qquad$ .
【Answer】 $55,60,65,70$
【Analysis】5 consecutive natural numbers must be a multiple of 5 (by the middle term theorem), the maximum sum of the five numbers is $45+6+7+8+9=75$: the minimum is $45+1+2+3+4=55$, so the possible values are $55,60,65,70,75$: when the sum is 75, we have $75=17+16+15+14+13$, and $17=9+8$, which leads to a contradiction. Construction: Sum is 55: Bei, Jing, Dong, Ao are $1,2,3,4$; Sum is 60: Bei, Jing, Dong, Ao are $1, 3, 5, 6$; Sum is 65: Bei, Jing, Dong, Ao are $3, 4, 7, 6$; Sum is 70: Bei, Jing, Dong, Ao are $5, 8, 3, 9$