填入所缺单词完成句子。
      Many years ago people didn't travel by ______________. They didn't travel by ______________.
They didn't travel by ______________.

参考答案：
bike, plane, train
答案不唯一

填入所缺单词完成句子。
      Many years ago people didn't travel by ______________. They didn't travel by ______________.
They didn't travel by ______________.

参考答案：
bike, plane, train
答案不唯一