CAT 2020 Sentence Correction and Error Correction — Previous Year Question

In the following question, four sentences are given which may contain grammatical or contextual errors. Choose the one which contains an error. If there is no error in any of the four sentences, mark (e) i.e. "All are correct":

A) The train has provided a trouble-free performance in the last six months. B) The unraveling had commenced even before Train 18's inaugural run as Vande Bharat Express. C) It is futile to expect the techno-bureaucracy of the Indian Railways to reform itself. D) The Centre made amendment in proviso to Article 370(3) as a part off a well-conceived strategy.