题目

The general objective of public interest advertising is to inform, persuade, or remind people about the particular idea, cause, or philosophy being advertised. This kind of advertising is often used by non-business institutions, such as schools, hospitals and charity organizations. We also see advertising by associations. In addition, we witness millions of dollars’ worth of advertising placed by government organizations. Much government advertising announces the availability of such valuable government services as consumer assistance, welfare aid, or career guidance. However, with th如图所示的四种情景中，属于光的直线传播的是 [     ]A．B．C．D．