Complex sentence: The main problem in this method is the selection of the index-whether the index should be Consumer Price Index or Wholesale Price Index (WPI) or Retail Price Index (RPI) or Index of Industrial Production (IIP) or any other index ?
Split into simpler sentences: The main problem in this method is the selection of the index. Whether the index should be Consumer Price Index or Wholesale Price Index (WPI) or Retail Price Index (RPI) or Index of Industrial Production (IIP) or any other index?