科学家一般用（）的变化作为观察脑活动的客观指标。
A.梦境
B.脑电波
C.睡眠
D.脑图像
参考答案：B
下列哪一种良性皮肤肿瘤易自行消退（）。
A.鲜红斑痣
B.草莓状血管瘤
C.海绵状血管瘤
D.汗管瘤
E.痣细胞痣
— Can you guess ______ the MP4 player yesterday?
— Sorry, I've no idea about it. [ ]
A. how much did he pay for
B. how can he get
C. how much he paid for
D. how much he pays
