7. (10 points) When the following vertical calculation is correct, the sum of the divisor and the quotient is ( )
A. 289
B. 351
C. 723
D. 1134
【Solution】Solution: First, according to the third last row, we can determine that $A=0, B=4$;
Then, based on the last digit of the third row being 1, we can determine that the values of $D$ and $C$ in the first row are $(1,1)$ or $(3,7)$ or $(9,9)$ or $(7,3)$.

Since the divisor's double is a four-digit number, the divisor must be greater than 500. Also, since the first result is a three-digit number, the only pair that fits is $(1,1)$ for $C$ and $D$.

Therefore, the tens digit of the quotient must be 4 to satisfy the units digit being 4, so the hundreds digit of the divisor can only be 5.
Then, based on the tens digit of the final four-digit number being 6, we can determine that the tens digit of the divisor is 8.
The dividend is $581 \times 142=82502.581+142=723$.
Therefore, the answer is: $C$.