Bob comes from England. He is eleven. He likes to play basketball. His father Mr Brown works in a big shop in Shijiazhuang. Bob has a brother. His name is Mike. He is only four.

    It is Saturday. Bob's family are all at home. Mr. Brown is sitting on a chair and reading a book. Bob is cleaning his new bicycle. His brother is playing with his dog.

蕨的结构比葫芦藓的结构复杂之处是（　　）

厨房里发生的下列变化中，属于物理变化的是

下图是某同学为测量金属丝电阻率连接的实物图，图中ab间接的是待测金属丝，P为可移动的线夹，R为定值电阻.