题目

日常生活中许多现象与化学有着密切联系，请选择适当的物质填空：医用酒精的溶剂是_________；冬天用煤火取暖，若通风不畅会发生中毒，是由__________引起的。 答案：水；  一氧化碳   In American, a friend inviting you to a restaurant doesn't mean that he or she will pay for the meal ______ you are told ahead.A．untilB．unlessC．althoughD．if