The Wholesale Price Index (WPI) is a measure of the price level of goods traded in bulk by manufacturers and producers. The base year is a specific year the government chooses as a reference point to calculate the WPI.

Option 1 suggests 1981-82 as the base year. Similarly, options 2 and 4 propose 1990-91 and 1994-95 respectively as the base year. These are incorrect choices as the government did not set the WPI base year as any of these during the referred period.

The correct answer is option 3, which suggests 1993-94 as the base year. This is the year the government of India chose as a reference for calculating the WPI for the new series released at the time.

However, please note that the base year of the WPI in India has been revised several times over the years to better capture inflation trends. The most recent base year, as of now, is 2011-12.