■ did

1) 中国人说英语以 Did... 开始的问句，如果学得不好，往往后面的动词仍然用过去式（应该用没有 to 的不定式），这是根本不通的。虽然这个错误容易发觉，但往往仍然冲口而出，但只要多练习就不难避免。例如：*Did you went to school yesterday? (Did you go to school yesterday?)

2) 如果 did 后面的动词是变位的，那就在正常情况下肯定不是以 did 为助动词，这个 did 肯定是代替前面一个实义动词的，例如 2003 年《纽约时报》因为一名黑人记者 Blair 凭空制造假新闻而出现丑闻，一位评论家 Richard Cohen 写文章谈到此事时指出了 Blair 的不良作风，然后说：

• That should have been enough to halt Blair's career in his tracks. That it didn't testifies to a newsroom culture, imposed from above, that cherished diversity—not more than accuracy, but so much so that journalistic standards were bent. (The Daily Gazette, Schenectady, New York, May 13, 2003)本来这种毛病会使得 Blair 的职业前途受阻。没有受阻，就说明了有一种从上往下强加的新闻编辑室风气，它一味注重多种族用人才，尽管并不以此压倒对新闻准确性的注重，但也到了使得新闻业务标准遭受扭曲的程度。

3) 但是， 2) 有一个例外，就是 used to inf. 如果否定，用了助动词 didn't 之后，used 仍然可以不还原为 use，而是仍然保持 used 的过去形式。

• I didn't used (didn't use) to like opera, but now I do.我过去不喜欢歌剧，但是现在却喜欢。

疑问句用了助动词 did 之后，used 也仍然可以不还原为 use。

• What did people used (use) to do in the evenings before TV?人们晚上看电视之前一般干些什么？