根据短文理解，完成下列各题。
Tom is five years old. He has no brothers or sisters. He is a lovely boy. He doesn't go to school because he is too young. He likes to play with other children in the small park every day.
The park is near his building. In the park there are interesting things to see and play with.
Tom's parents love him very much. They often buy him nice things. This time, his mother buys some new clothes for him. The clothes are expensive and nice. Tom is very happy to wear them.
“Mum, can I go out and play with my friends? I want them to see my new clothes,” asks Tom. “All right, but please keep your clothes clean,” says Mum. “I am going to do some cooking. We will have supper after your father comes back.” At about six, his father comes back from work. And Tom goes home for supper.
“Why do you have much earth (泥土) on your clothes?” asks his mother.
“Because I have some falls(摔跤), ” answers Tom. “You should not make the nice clothes dirty” Mother says.
“I'm sorry, Mum” says Tom, “But I have no time to take off my clothes when I fall.”
Sn2＋(aq)＋Pb(s)，体系中c(Pb2＋)和c(Sn2＋)变化关系如图所示。下列判断正确的是( )
