题目

根据短文理解，选择正确答案。 My husband and I are saving thousands of dollars every year by growing our own vegetables in our backyard. We learn something new every year and this website has been made to share tips with other people that would like to grow some of their own food. It's true that if you are starting from fresh, it will cost a little bit of money to get started. However, once everything is set up, the cost is very small and the rewards are huge. The size of your family and how many vegetables you eat determine exactly how much money you can save every year. We do a 入冬以来，合肥多次出现雾霾天气，PM2.5浓度飙升。PM2.5是指大气中直径小于或等于2.5μm的颗粒物，富含大量的有毒、有害物质，易通过肺部进入血液。目前PM2.5已成为空气污染指数的重要指标。下列推测合理的是（ ）A．PM2.5进入人体的肺泡中时还没有进入人体的内环境B．颗粒物中的一些酸性物质进入人体血液会导致血浆呈酸性C．PM2.5可能成为过敏原，其诱发的过敏反应属于机体免疫能力较低导致的免疫异常D．颗粒物进入呼吸道引起咳嗽属于非条件反射，其调节中枢在下丘脑