Which one is the proper tag question in the following sentence:
He always lags behind ______?

The proper tag question for the sentence "He always lags behind" is "doesn't he?"

Explanation:
In this case, the main sentence "He always lags behind" uses the present simple tense with a negative meaning implied by the verb "lags behind." When forming the tag question, you invert the auxiliary verb and subject of the main sentence. Since the main verb is in the present simple tense, the auxiliary verb "does" is used, and it is negated to "doesn't" to form a contrasting question tag. Hence, "doesn't he?" is the appropriate tag question.

• "Did he" is incorrect because the main sentence is in the present tense ("lags"), so the tag question should also be in the present tense.

• The usual form is with the contracted "doesn't."

• "Did not he" is not only in the past tense, which doesn't match the tense of the main sentence, but it's also not the standard form for a tag question.

• "Would not he" is inappropriate because it introduces a conditional mood, which is not present in the main sentence.

Therefore, the correct tag question is "doesn't he?" to match the present tense and negative form required for a tag question.