The correct answer is A. Indian scholars invented all of the following that we use today except the 12 month calendar.
Regarding the 12-month calendar, this was not invented by the Indians.
In ancient civilizations, the lunar calendar was used to calculate the passage of time. The transition between one month and another was marked by the orbit of the Moon: when it returned to its initial phase, this time period was considered to be over. After 12 lunar months, there was talk of a full year. Some time later, the need to take into consideration the passage of the seasons arose, and lunisolar calendars were created, which grouped the lunar months in different climatic periods.
In Ancient Egypt, the first solar calendars appeared, which measured the time guided by the apparent movement of the Sun. This innovation allowed to date the exact moment of the flood of the Nile River, fundamental for a society that lived on agriculture. Egyptian astronomers knew that the year lasted 365 days, but they did not consider those few extra hours that do not complete a day. The Egyptian calendar thus carried with centuries of lag, and religious opposition slowed down any hint of reform.
At the time of the Roman Empire, the calendar had 304 days arranged in 10 months, so that the pontiffs had to interject an eleventh month every few years to compensate for the temporary imbalance. This, however, increased to the point that winter ended up being dated in the astronomical autumn. Julius Caesar, in 46 BC, ordered a reform of the Roman calendar in order to definitively adjust the year to the course of the Sun. The Julian calendar, which retained the 365 days divided into 12 months of the Egyptian calendar, dated the seasons and its corresponding Roman festivals agreeing with the astronomical moment in which they happened. To counteract the lag, instead of interspersing one month every X time, it was decided to add one day every four years (including the secular ones), which originated the concept of a leap year.
