Introduction:
The given question asks to arrange the events in sequential order as they happened in India. The events mentioned are the Mahalanobis Model, Plan Holiday, and Rolling Plan. Let us analyze each event and arrange them in the correct order.

Explanation:

1. Mahalanobis Model:
The Mahalanobis Model refers to the Second Five-Year Plan (1956-61) introduced by the Indian government. This plan was formulated by the renowned economist Prasanta Chandra Mahalanobis, who aimed to promote industrialization and economic growth in India. The plan focused on achieving self-sufficiency in industries, reducing dependence on imports, and modernizing the country's infrastructure. It emphasized the establishment of heavy industries and the development of scientific and technological capabilities.

2. Plan Holiday:
The Plan Holiday refers to a period between 1966 and 1969 when no Five-Year Plans were implemented in India. This break in planning was primarily due to the severe economic crisis faced by the country during that period. India was grappling with food shortages, stagnating agricultural productivity, and a balance of payment crisis. The government decided to reassess its economic policies and strategies during this time.

3. Rolling Plan:
The Rolling Plan refers to the strategy adopted by the Indian government after the Plan Holiday. It was introduced in 1978 and aimed to have a continuous planning process rather than rigidly following fixed five-year plans. Under this approach, the plans were formulated for a shorter time frame and were extended or modified based on the changing circumstances. The Rolling Plan allowed for flexibility and adaptability in response to economic and social developments.

Arranging the Events:

Based on the above explanations, the correct sequential order of the events is as follows:

1. Mahalanobis Model (Second Five-Year Plan, 1956-61)
2. Plan Holiday (1966-1969)
3. Rolling Plan (Introduced in 1978)

Therefore, the correct answer is option 'A' - 1, 2, 3.