Fill in the blanks with the most appropriate words.
When _____ the watchman _____ work?
A verb is used to express an occurrence, action, or state. It is the grammatical centre of the predicate in a sentence.
An auxiliary verb is a verb which gives is used in the formation of tenses, moods, tones, etc.
Option B is correct as the subject is singular and when followed by a blank indicates the use of past simple tense. As the question is in the past simple tense, did is used in the first blank and indicates the use of start in its first form.
The other options are wrong as the main verb (start) can only be used in its first form.
The correct answer is B) did/start