What does the imagery in the passage show about doodle?

If you are referring to the passage where Doodle is a baby and trying to get up when laid on his stomach, then his determination would be the correct answer.
The excerpt is telling us how Doodle wanted to succeed in moving on his own despite the many difficulties that he encountered because of his weak heart. He never gave in to his inabilities which is why he is considered to be hard-working and bent on achieving his goals. Based on this explanation, I believe the correct answer is - He is determined and does not give up easily.