You are welcome to answer questions posted in the Ask a Teacher forum as long as your suggestions, help, and advice reflect a good understanding of the English language. If you are not a teacher, you will need to state that clearly at the top of your post. Please note, all posts are moderated by our in-house language experts, so make sure your suggestions, help, and advice house the kind of information an international language teacher would offer. If not, and your posts do not contribute to the topic in a positive way, they will be subject to deletion.
In this construction "did" is an auxiliary verb in the past tense. The auxiliary do/does/did takes the base (infinitive) form of a verb. Tense is reflected in the auxiliary.
error analysis 
Linear Mode
