表达应该做与不应该做的句型 — 英语情景题

情景对话：Sam 和 Lily 在公园里看到一个男孩想摘花。 Sam: Look! The boy wants to pick the flowers. Lily: He (1)________ not pick the flowers in the park. Sam: You are right. And we (2)________ keep off the grass, too. Lily: Yes. We should (3)________ the right thing in public places. Sam: What should we do if we see someone littering? Lily: We should tell him, "Don't (4)________, please."