I have a good friend. His name is Nick. He is a middle school student.  He usually 1 at 5:30 every day. Then he has 2 quick breakfast and 3 to school at six. He usually goes to school by bus. First he 4 to the bus stop. Then the bus takes 5 to school. It usually takes him forty minutes6 to school.

    My home is about two miles from school. I usually leave for school at about 6: 30. I usually get to school 7 It takes me about twenty 8 But sometimes I got there by bike.  It takes me only ten minutes.

    There are different 9 to get to school. But I like10 best.

为了便于记忆历史知识，我们常用简洁的词语来总结某一时期的主要建设成就。“一桥”“二铁”“三藏”“四厂”总结的是我国哪一时期的建设成就（    ）