1. (10 points) The sum of the digits of the product of 45 and 40 is ( )
A. 9
B. 11
C. 13
D. 15
【Analysis】According to the problem, first find the product of 45 and 40, i.e., $45 \times 40$, and then add up the digits of the resulting product.

【Solution】Solution: According to the problem, we have:
$$
45 \times 40=1800 ;
$$
The sum of the digits of 1800 is: $1+8+0+0=9$;
Therefore, the sum of the digits of the product of 45 and 40 is 9.
Hence, the answer is: $A$.