【Answer】1
【Analysis】Key point: Number decomposition
Multiples of 5 are only 5 and 10, so $\mathrm{E}+\mathrm{F}$ can only be $6, 4 / 4, 1 / 3, 2$.
When $E, F$ are 6 and 4, C, D are 1 and 2, A, B are 3 and 5, which meets the requirements.
C, D are 1 and 5, A, B are 3 and 2, which does not meet the requirements.

When $E, F$ are 4 and 1, C, D can only be 3 and 6, at this time A, B are 2 and 5, which does not meet the requirements.
When $E, F$ are 2 and 3, C, D are 1 and 5, at this time A, B are 4 and 6, which meets the requirements.
C, D are 4 and 5, at this time A, B are 1 and 6, which does not meet the requirements.
In summary, the smaller number of C, D is 1.
16. Fill in 1 and 6 in the three equations on the right, using each number exactly once, so that $\mathrm{A}+\mathrm{B}$ is a multiple of 2, $\mathrm{C}+\mathrm{D}$ is a multiple of 3, and $\mathrm{E}+\mathrm{F}$ is a multiple of 5. Then the smaller number in $\mathrm{C} 、 \mathrm{D}$ is $\qquad$ (fill in the specific number)