10. Chaoyang Electrical Factory and Hongxing Electrical Factory had equal output values in January 2005. The output value of Chaoyang Electrical Factory increased monthly by a constant amount, while the output value of Hongxing Electrical Factory increased monthly by a constant percentage. It is known that in January 2006, the output values of both factories were equal again. Then, in July 2005, the factory with the higher output value is ( ).
(A) Chaoyang Electrical Factory
(B) Hongxing Electrical Factory
(C) Both factories are the same
(D) Cannot be determined
10.A.

Let the output value of two factories in January 2005 be $a$, the monthly increase in output value of Chaoyang Electrical Factory be $d$, and the output value of Hongxing Electrical Factory be $q(q>1)$ times that of the previous month, then
$$
a+12 d=a q^{12} .
$$

The output values of the two factories in July 2005 are $a+6 d$ and $a q^{6}$, respectively.

And $a+6 d=a+\frac{1}{2}\left(a q^{12}-a\right)=a \frac{q^{12}+1}{2}>a q^{6}$, so the factory with the higher output value is Chaoyang Electrical Factory.