There will be fewer workers in factories because most work _____ by robots in the future.
考查时态和语态。
句意:未来工厂里会有更少的工人,为大多数工作由机器人去做。主语 most work 与谓语动词被动关系,by 引出动作的执行者,要用被动语态;由时间状语 in the future 可知用一般将来时。故选选项C。
Don't forget _____ goodbye to him before you leave.
句意:在你离开之前不要忘记向他告别。表示“向某人告别”要用 say goodbye to sb. 的搭配,先排除选项B和选项D;再根据本题语境可知,“向他告别”这件事还没有发生,故要用 forget to do sth. 的搭配,故答案为选项C。