In Jack London's "The Call of the Wild," Buck undergoes significant changes from the beginning to the middle of the text. Initially, Buck lives a comfortable and privileged life as a pet in a wealthy household in California. However, as the story progresses, he is thrust into the harsh realities of the Yukon during the Klondike Gold Rush, where he experiences cruelty and harsh treatment at the hands of humans.
Given your options, the most accurate description of Buck's change from the beginning to the middle of the text would be:
He goes from a life of luxury to being a dog that is treated very cruelly.
This transformation marks the beginning of Buck's journey into survival and adaptation in a harsh environment, setting the stage for his further evolution.