Little Johnny...

Little Johnny had not studied for his life science exam.
The teacher in the one room school house was giving an oral exam.
"What are the four main advantages of breast milk?" she asked.
"No need to boil." called one student."
And another?" the teacher questioned.
"It never goes sour." said another child."Correct." said the teacher.
"It is available whenever is necessary." called out another.
"Johnny." she asked. "Do you have the last answer?"
"Sure," he said. "It is available in attractive containers of varying sizes."
He got an "A".