题目

Tom goes everywhere with Catherine Green, a 54-year-old secretary. He moves around her office at work and goes shopping with her. Most people don't seem to mind Tom, says Catherine, who thinks he is wonderful. He's my fourth child, she says. She may think of him and treat him that way as her son, buying his food, paying his health bills and his taxes, but in fact Tom is a dog.     Catherine and Tom live in Sweden, a country where everyone is expected to lead an orderly life according to rules laid down by the government, which also provides a high level of care for its people. This 下列自变量与因变量的关系，不能用图曲线表示的是A.氧气浓度与人体细胞二氧化碳产生速率B.被转运物质浓度差与主动转运速率C.底物浓度与酶促反应速率D.被转运物质浓度差与易化扩散速率