—How long have you __________ here?
—For two days. I __________ here the day before yesterday.
A:been; came
B:come, came
C:came; came
D:come, was
下列化合物中,既能发生消去反应生成烯烃,又能发生水解反应的是( )
阅读课文《大自然的语言》6、7小节,回答
大自然又告诉我们什么语言?