The type of levelling operations carried out for laying a railway track are1. Longitudinal levelling (L. S.)2. Fly levelling3. Barometric levelling4. Cross-sectioningSelect the correct answer using the codes given below:

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