"Breast milk" joke

Leonard desperately wanted to become a doctor and had really crammed for
his medical boards exams, so he wasn't in the least fazed by the question:

"Name the three advantages of breast milk."

Quickly he wrote:

1. It contains the optimum balance of nutrients for the newborn child.

2. As it is contained within the mother's body, it is protected from
germs and helps develop the child's immune system.

Then Leonard was stumped. Sitting back and racking his brain until he'd
broken into a sweat, he finally scribbled:

3. It comes in such nice containers.