题干
------ Have you seen your nephew lately?
------ Yes, in fact, I saw him yesterday. I ______ him for three years.
------ Yes, in fact, I saw him yesterday. I ______ him for three years.
A：haven’t
B：didn’t
C：hadn’t
D：don’t
答案(点此获取答案解析）
C
2SO3(g)（正反应为放热反应），能使SO3的产量增加的措施是（ ）