Student or Learner
Is did a helping verb in the sentence "They did not complete the task." ?
That is one way to think of it.
The positive version is "They completed the task."
To make it negative, we require the right form of "to do" -- "They did not complete the task."
You also need the right form of "to do" to ask a question. "Did they complete the task?"
Note the form of "to do" (do, does, did) will depend on the person, number, and tense of the original positive statement.
Last edited by bhaisahab; 10-Jun-2015 at 21:04. Reason: Correct small typo.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.