The librarian told me that I could ___ these magazines for three days.
A:borrow
B:buy
C:keep
D:return
某人骑自行车由南向北行驶,这时有辆汽车也由南向北从他身旁疾驰而过,若以这辆车为参照物,此人( )
下列哪种地貌是黄土高原农业较发达,人口集中的地区( )