Select the most appropriate option to improve the bold part of the sentence.
No sooner I reached the platform than the train left.

Correct option is D

The correct substitution of the highlighted words is (d) No sooner had I reached.
Explanation: When a sentence begins with No sooner, we require subject–auxiliary inversion and typically use the past perfect to show the earlier of two quick, successive past actions: No sooner had + subject + past participle + than + past simple. Hence, No sooner had I reached the platform than the train left. (जैसे ही मैं प्लेटफ़ॉर्म पहुँचा, ट्रेन चल पड़ी।)
Grammatical rule used:
· Structure: No sooner + had + S + V³ + than + S + V².
· Use than (not then/but) to introduce the second clause.
· Example: No sooner had she opened the door than the phone rang.
· Information booster: A correct alternative pattern is No sooner did + S + V¹ + than + past simple (e.g., No sooner did I reach than…), but with reached given, option (d) best fits the conventional past perfect structure.