The Boo baby has learned to roll . He rolled from tummy to back the first time when he was about a week old and has done it a few times since . About three weeks ago he figured out how to roll from back to tummy over his left side , and he 's been a rolly - poly boy ever since . Now , when we lay him in the floor , he will roll back to tummy to back to tummy over and over again .
Why did the baby roll back and forth ?
Pick the best answer from the following options:
- None of the above choices .
 - He was learning to walk .
 - He was learning to sit up .
 - His clothing was uncomfortable .


He was learning to sit up .