题干
— There ___________ a picture on the wall for a long time.
— Oh, right. It's so beautiful.
A：have had
B：has had
C：have been
D：has been
答案(点此获取答案解析）
D
— There ___________ a picture on the wall for a long time.
— Oh, right. It's so beautiful.
A：have had
B：has had
C：have been
D：has been
，符合这一条件的烯烃有（ ）
2NH3的正、逆反应速率可用各反应物或生成物浓度的变化来表示。下列各关系中能说明反应已达到平衡状态的是