Consider the following statements:1. The normal annual rainfall of a station is obtained as the arithmetic average of the successive annual rainfall in the last 30 years.2. The “normal rainfalls” are updated by deleting the needful number of oldest years’ data from the record and adding the needful number of most recent years’ data to the record.3. The standard deviation computed for the rainfall data is taken as a measure of the variability of the rainfall during the self-same set of years.4. If the observed rainfall in any year is less than the current average annual rainfall, then that year is called a dry year.Which of the above statements are correct?

• A. 1, 2, 3 and 4
• B. 1, 2 and 3 only
• C. 2 and 4 only
• D. 1, 3 and 4 only