如图所示，甲是用“伏安法”测量未知电阻R_x的实物电路图．

完形填空。

    Tom and his father are 1 in the playground. There is a cat and a dog there.  They are playing with a ball together. “I think the cat is 2 than the dog," Tom says, “I don't think so," his father says. “Why?"  “Because the dog looks 3 than the cat " Tom laughs and says, "But I like the cat.  It is white and it is 4 than the dog. " Tom's father says, “Dogs are my favourite animals because they are very 5 to me " "Yes, but I like smaller ones. Can we keep one?" Tom says. "of course," Tom's father says.