What were the main challenges that the central pacific faced in completing its parts of the transcontinental railroad?

What does the simile add to the passage

Read this excerpt from white fang by jack london. the qualities in his kind that in the beginning made it possible for them to come in to the fires of men, were qualities capable of development. they were developing in him, and the camp-life, replete with misery as it was, was secretly endearing itself to him all the time. but white fang was unaware of it. he knew only grief for the loss of kiche, hope for her return, and a hungry yearning for the free life that had been his. which quotation from the paragraph supports the story’s theme of homesickness? “the camp life . . was secretly endearing itself to him all the time.” “but white fang was unaware of it.” “he knew only . . a hungry yearning for the free life that had been his.” “the qualities in his kind . . were qualities capable of development.”

Which verb from is used to indicate the perfect progressive tense