世界上全部位于北半球的大洲是（）
A.欧洲.北美洲
B.亚洲.欧洲
C.非洲.北美洲
D.大洋洲.亚洲
参考答案：A
Our teacher asked me ________.
A．what was Ann doing these days
B．why didn’t Peter come to school the day before
C．when will the dolphin show begin
D．how long I usually spent on my homework
某种电池的正极材料由锂（Li）、钴（Co）和氧元素组成，三种元素的化合价分别为+1、+3、-2，则该物质的化学式为
A．LiCoO
B．LiCoO2
C．LiCoO3
D．LiCoO4
