A:逐水草而居
B:地势平坦
C:开发矿产资源
D:土地资源丰富
The dictionary as well as the grammar books that ________ bookmarks in them ________ Jane.
根据汉语提示将下列英语句子补充完整,每空词数不限。
已知a→=3,b→=23,a→·b→=-3,则a→与b→的夹角是( )