题干
Why not ____ your teacher for help when you can't finish _____ the story by yourself?
A：to ask; write
B：to ask; to write
C：ask; writing
D：asking; to write
答案(点此获取答案解析）
C
Cl、
Cl两种同位素，若知氯元素的相对原子质量为35.5，则