交通方式表达：by plane, by train — 英语词汇题

根据中文提示补全句子（每空一词）。1. Going by train is slower, but it is cheaper than going ______ ______（乘飞机）. 2. My family lives far from here. We usually go to my grandparents' home ______ ______（乘火车）because it is safe. 3. The city is very far away. ______ ______ ______ takes only two hours.（乘飞机）