Answer: He is determined and does not give up easily.
Step-by-step explanation:
Imagery is a literary device whereby a figurative language is used to evoke a sensory experience in the mind if the reader or audience.
In thus case, the underlined imagery in this excerpt show that Doodle is determined and does not give up easily.
Despite the fact that the doctor said that with his weak heart, he could be killed by the strain, but it didn't. He would push himself up, and eventually learned to crawl and survived.
This showed that he is determined and does not give up easily.