had better提建议的用法 — 英语词汇题
题目
根据句意及所给提示，用 had better 的正确形式完成句子（每空一词）。在公园野餐后，你看见弟弟正要把垃圾扔在草地上，你想劝阻他并提醒他爱护环境：There is a bin over there. You ________ ________ ________ (not litter) on the grass, or you'll be fined. Besides, keeping the park clean is good m________（礼貌，复数）.