— Laura, we've decided on a trip this afternoon. Will you join us?
— I’m afraid not. I have a composition .
A:to go; to write
B:to go; writing
C:going; to write
D:going; writing
Nobody can live________ fresh air and clean water.
西瓜和西瓜子分别是由( )发育而成的.
下列关于线粒体和叶绿体的共同点的叙述,错误的是( )