Select the most appropriate option to improve the bold part of the sentence.
Hardly I had entered the room when the phone rang.

Correct option is A

The correct substitution of the highlighted words is (a) Hardly had I entered.
Explanation: With negative/limiting adverbs like Hardly/Scarcely/No sooner placed at the beginning, subject–auxiliary inversion is required. The earlier action (“entering”) takes the past perfect and the subsequent action (“the phone rang”) takes the simple past, joined by the appropriate correlative ( when/than). Hence, “ Hardly had I entered the room when the phone rang.”
Grammatical rule used:
· Hardly/Scarcely/Barely + had + subject + V³ + when/before + simple past
· No sooner + had + subject + V³ + than + simple past
· Example: “ No sooner had the meeting started than the fire alarm went off.”
· Information booster / exceptions: If Hardly is not fronted, inversion isn’t needed (e.g., “I had hardly entered when …”), but since the adverb starts the sentence here, inversion is mandatory. Options (b), (c), and (d) break either the tense sequence, the inversion requirement, or the idiomatic pairing with when/than.