题目

Like most people, I’ve long understood that I will be judged by my occupation, that my profession is a standard people use to see how smart or talented I am. Recently, however, I was disappointed to see that it also decides how I’m treated as a person.Last year I left a professional position as a small-town reporter and took a job waiting tables. As someone paid to serve food to people, I had customers say and do things to me I suspect they’d never say or do to their most casual acquaintances（泛泛之交）. One night a man talking on his cell phone waved me away, then asked me back w科学家做过这样的实验：准备好含Ca2＋、Mg2＋和SiO44－的培养液，将番茄和水稻分别放在上述培养液中培养。一段时间后，培养液中的离子浓度如图所示。根据实验结果，以下结论正确的是A. Ca2＋、Mg2＋和SiO44－的跨膜运输是顺相对含量梯度的B. 细胞对于物质的输入和输出具有选择性C. 不同作物对无机盐的吸收差异不大D. 番茄培养液中的SiO44－离子浓度增高是由于番茄体内的SiO44－外流所致