so:
Mouse on object SpriteA clicked - audio play = "A"
The other way around you could set a global variable "Letter" to choose("A","B","C", etcetera)
On pressed button play - audio play = global variable "Letter"
On spriteA clicked
system compare global variable "Letter" = "A"
set text to: "Congratulations!"
I hope that with this explanation you can get started.