The correct answer to this question is "D) India's Independence." Let's examine why:
Nectar in a Sieve was published in 1954 and, thus, was written by Kamala Markandaya in the time leading up to this date. The Salt March happened in 1930 when Gandhi led a peaceful protest in order to unite Muslim and Hindu Indians against the colonialist influence of Great Britain, which held a monopoly on India's salt. This event preceded the book's publication by 24 years, which doesn't fit the description of "shortly before" stated in the question.
In regards to timing, the same can be said for the Sepoy Rebellion, which occurred in 1857 in response to the rule of the British East India Company. It is also known as India's First War of Independence.
The Green Revolution began in the early 1960s and generated an increase in food grain production. This shift in agriculture occurred after the publication of the book.
That leaves us with India's Independence, which occurred in 1947—a mere seven years before the book was published.
Since Kamala Markandaya's novel was published in 1954, the correct answer to your question would be India's independence, which occurred in 1947. Effectively, two hundred years of British rule was ended in that year, with British India divided into the nations of India and Pakistan.
The other three answers are not correct because:
a) Gandhi's Salt March occurred on March 12, 1930. The march was a protest against the British monopoly of salt production in India. Indians had to purchase salt at a significantly higher price from the British because they were not allowed to process salt locally. Gandhi hoped that his peaceful salt protest would focus Muslim and Hindu efforts on defying colonial rule instead of on sectarian infighting.
b) The Sepoy Rebellion occurred in 1857. History tells us that the sepoys rose up against the rule of the British East Indian Company because they were angered by the British appropriation of power in local states/districts. With the growing presence of missionaries, the sepoys also became alarmed that the British may have been trying to convert all Indians into Christians.
c) The Green Revolution in India occurred in the 1960s and the 1970s. This was a revolution in agriculture between 1967 to 1978 which propelled India to the forefront of agriculture production on the global stage.
The Green Revolution in India