निम्नलिखित में से कौन सी आर्थिक गतिविधि द्वितीयक क्षेत्र (secondary sector) के अंतर्गत आती है?

Which institution maintains the buffer stocks of wheat and rice in India?

Consider the following statements regarding the Consumer Price Index (CPI) and its implications: I. The revised CPI aligns item weights with recent Household Consumption Expenditure Survey (HCES) data, better reflecting current consumption patterns. II. Under the revised index, services-related components (such as housing, health, education, and transport) carry a higher relative weight than earlier, improving the index's sensitivity to services inflation. III. A change in the CPI base year alters the measured inflation rate by itself, even if prices of all goods and services remain completely unchanged. IV. State-level inflation differentials under the revised CPI reflect differences in consumption structures in addition to food price movements. How many of the above statements are correct?