行为规范类词汇与短语 — 英语阅读题

Read the passage and answer the question. It is Monday morning. Lily is on the bus to school. The bus is full, so an old grandma is standing. Lily stands up and says, "Please take my seat." Then a boy throws a banana skin on the floor of the bus. Lily tells him, "Don't litter here. We should keep the bus clean." The boy's face turns red. He picks up the banana skin and puts it in the bin. When Lily gets off the bus, she waits in line and crosses the road at the zebra crossing. Question: What does Lily ask the boy NOT to do on the bus?