Hi!
The correct option is A.
The formation of memory is associated with formation of neural pathways or connections in the brain. For any new memory formed, a new neural pathway develops. Repetition serves to ensure that these pathways are well developed and established.
For a child to associate a particular sound with a meaning, repetition not only serves to reinforce the concept, but also ensures that the neural pathway to that information in a child is well developed and that the child is quickly able to recall the meaning from memory on hearing the sound.
Hope this helps!