具有镇痛作用的物质是
A.钾离子
B.β内啡肽
C.缓激肽
D.乙酰胆碱
E.组织胺
参考答案:B
We don''t plan to go to the concert, and so they don''t .
A.so do they
B.they don't too
C.neither don't they
D.they don't either
电子商务可以分为以下哪3种类型()
A.B2C
B.C2C
C.B2B
D.B2G