A coastal forecasting model consistently predicted stronger winds than nearby weather stations recorded. Only after meteorologists compared data from weather balloons with satellite measurements ______ that a calibration error in one station, rather than a flaw in the model, accounted for the discrepancy.
Which choice completes the text so that it conforms to the conventions of Standard English?
When a sentence begins with a restrictive or negative expression such as “only after,” “only when,” or “not until,” check whether the following main clause requires subject-auxiliary inversion. If the sentence uses “did” for inversion, remember that the main verb must remain in its base form.
Hints
Examine the opening words
Consider how beginning a sentence with a restrictive expression such as “only after” affects the order of the main clause.
Locate the subject and verb
Identify “the research team” as the subject and determine whether an auxiliary verb should appear before or after it.
Check the verb following an auxiliary
If a form of “do” is used as an auxiliary, consider which form of the main verb must follow it.
Step-by-step Explanation
Identify the introductory clause
The second sentence begins with the fronted adverbial clause “Only after meteorologists compared data from weather balloons with satellite measurements.”
Apply subject-auxiliary inversion
When an expression such as “only after” is placed at the beginning of a sentence, the main clause uses subject-auxiliary inversion. An auxiliary verb must therefore come before the subject “the research team.”
Use the correct form after the auxiliary
The past-tense auxiliary “did” is followed by the base form of the main verb, producing “did the research team conclude.”