题目

阅读理解 My name is Cindy. I'm thirteen years oldthis year, I'm a middle school student. I'm in Class Three, Grade Seven, I havetwo new subjects this year. They are science and history. My favorite day isThursday because I have science on that day. I have a twin sister. Her name is Sonia.She is also a middle school student. She is in Class Six, Grade Seven, Shelikes English. Her favorite day is Monday because she has English on that day. My father is Mr. White. He is a mathteacher. His favorite day is Sunday because he can go to the baseball club. Helikes playing baseball. My mother is Mrs 解答题 用水清洗一堆蔬菜上残留的农药．对用一定量的水清洗一次的效果作如下假定：用1个单位量的水可洗掉蔬菜上残留农药量的，用水越多洗掉的农药量也越多，但总还有农药残留在蔬菜上．设用x单位量的水清洗一次以后，蔬菜上残留的农药量与本次清洗前残留的农药量之比为函数f(x)． (1) 试规定f(0)的值，并解释其实际意义； (2) 试根据假定写出函数f(x)应该满足的条件和具有的性质； (3) 解：设f(x)＝，现有a(a＞0)单位量的水，可以清洗一次，也可以把水平均分成2份后清洗两次，试问用哪种方案清洗后蔬菜上残留的农药量比较少?说明理由．