若关于x的二次函数y=x²-3mx+3的图象与端点为$A\left(\frac{1}{2},\frac{5}{2}\right),B\left(3,5\right)$的线段（包括端点）只有一个公共点，则m不可能为(   )

如果a＞b，c＜0，那么下列不等式成立的是（      ）

    Every ____(秋天)I go to visit my grandparents．They live in the countryside．It takes me____(四十)minutes to get there by train．They have a big____(农场)．I always spend much time staying with different kinds of animals and____(植物)in it．From day to night，I have many____(有趣的) things to do．Sometimes，I climb trees and draw some pictures of beautiful flowers．Sometimes，my____(爷爷)and I feed the animals such as our dog，cows，chickens and ducks，He____(帮助)me know a lot about them．It is also great fun to see the little ____(黄色的)chickens eating noodles and ducks swimming in the river．In the countryside，I can____(学习)a lot from playing．I am never____(劳累的)of the days there．

平常的物体不带电的原因是（　　）