有一读者问：有这样一句话： It is true that you can't see your books and the blackboard. 我认为此句中的连词 and 应改为 or，不知正确与否？
如果上下文清楚，不会产生歧义，这句话用 and 也是可以的。 但 and 用在否定结构中往往会有歧义，如：
(1)I don't know A and B.
这句话意味着：
(2)I don't know A and I don't know B either.
也可能意谓：
(3)I don't know both of them. I only know A.
再如：
(4)She didn't speak clearly and correctly.
这句话可能意谓：她讲的既不清楚也不正确。但也可能意谓：她讲得清楚，但不正确。在这种情况下，为了避免误会，就应该或说：
(5)She didn't speak clearly or correctly.
或说：
(6)She spoke clearly, but not correctly.
但有时并不会产生歧义，如：
(7)Bob didn't break the window and refuse to apologize for his action.
(8)In China's feudal past almost nothing was said about democracy and the rule of law.
