Select the correct option:
Only after a decade of fieldwork __ fully grasp the dialect’s nuances.

Correct option is B

The correct option to fill in the blank is (b) did she.
This sentence begins with “Only after…”, a negative/limiting adverbial phrase that triggers inversion (auxiliary verb before subject). Since the main verb is in base form “grasp”, we use the auxiliary did for past reference: Only after… did she grasp… (Hindi meaning: उलट क्रम/इनवर्ज़न)
Example: Only after the results came out did he realise his mistake.
Explain why other options are incorrect:
· (a) she had: no inversion; also would require a different structure like “she had fully grasped.”
· (c) had she: would be correct only if the main verb were past participle: “had she fully grasped…” (not “grasp”).
· (d) she did: no inversion; after “Only after…”, inversion is required.
Information booster / exception:
· Inversion is compulsory with: Only then, Only after, Rarely, Seldom, Never, No sooner, Hardly/Scarcely (when placed at the start).
· Pattern: Only + time/condition + auxiliary + subject + main verb