To answer this analogy question, we need to find the relationship between the first pair of words (horse and ?) and then apply the same relationship to the second pair of words (board and ?).
In the first pair, a horse can be mounted, meaning someone can get on top of it to ride. Therefore, the relationship between "horse" and the missing word is that the missing word can be mounted.
Looking at the options:
A) "Stable" does not fit the relationship because a stable is where a horse is kept, not something that can be mounted.
B) "Shoe" also does not fit the relationship because a horse can wear shoes, but you cannot mount a shoe.
C) "Ride" fits the relationship because you can ride a horse, but it does not fit the analogy because it is the action performed on a horse, not something that can be mounted.
D) "Mount" fits the relationship because you can mount a horse, and it also fits the analogy because it is something that can be mounted.
Therefore, the correct answer is D) "Mount" because it completes the analogy: horse : mount :: board : train.