A：奴隶制
B：封建主义
C：资本主义
D：社会主义
我国素有“世界屋脊”之称的高原是（ ）
In my driving lesson, I learned a traffic rule that at no time _____ parked in a manner which will block emergency service.
①地狭人稠,人均资源不足 ②岛内市场狭小
③资金短缺,技术力量薄弱 ④山地多,交通运输落后
