Why does the author of "lifeboat ethics" choose to begin his essay with this lifeboat metaphor?

Buck did not cry out. he did not check himself, but drove in upon spitz, shoulder to shoulder, so hard that he missed the throat. they rolled over and over in the powdery snow. spitz gained his feet almost as though he had not been overthrown, slashing buck down the shoulder and leaping clear. twice his teeth clipped together, like the steel jaws of a trap, as he backed away for better footing, with lean and lifting lips that writhed and snarled. read this passage. explain what the conflict shows about buck and spitz.

Dogs make wonderful pets because they us stay happy and healthy. the topic sentence is "dogs make wonderful pets." , is this correct? i keep doubting myself.

The greatest gift the sumerians gave the world was the invention of writing. the sumerians were a wealthy people. they needed some way to keep track of what they owned. they began drawing pictures. they used a reed as a pen. they drew on soft pieces of clay. the soft clay was then dried in the sun. the tablet became a permanent record. later, the sumerian drawings changed into wedge-shaped symbols. this kind of writing is called cuneiform. by putting symbols together, the sumerians could write entire sentences.