A+D = P

There once was a lonely A  
who thought no one could see
Since she had two sisters that
attracted attention equally
 
One day, a D came along
and spotted the A. Wondered should
he give it a twirl
or be on his way
 
Then, as quick as a thought could be
P whispered, "A is for you. Give it a try and see."
 
So D went to A, and P was pleased as can be
No one ever thought
 
A+D = P