Fill in the blanks with the most appropriate option:-

The construction of this skyscraper had been going on ………India won the world cup.

since

The correct option to fill in the blanks is since.

The sentence is about the construction of a skyscraper that started before India won the world cup and was still ongoing at the time of India winning the world cup. The preposition "since" is used to indicate a point in time from which something has been happening. It is the most appropriate preposition to use in this context, as it describes the fact that the construction of the skyscraper started before India won the world cup and is still ongoing.

The other options are not as appropriate:

• From can be used to indicate a starting point, but it does not convey the same sense of continuity as "since".
• When can be used to indicate a point in time, but it does not convey the same sense of duration as "since".
• Till can be used to indicate a point in time up to which something happened, but it is not as appropriate as "since", as it does not convey the same sense of continuity.