题干
Only when ________ be possible to sign the papers.
A：does the boss come will it
B：the boss comes will it
C：has the boss come it will
D：the boss comes it will
答案(点此获取答案解析）
B
表示氧原子， 
表示氢原子．根据此图，试分别从物质组成、分子构成、物质变化的角度各说出一种观点． 