Which of the following statements about optical microscope is/are correct? 
1) Both the eyepiece and objective of a microscope are convex lenses. 
2) The magnification of a microscope increases with increase in focal length of the objective. 
3) The magnification of a microscope depends upon the length of the microscope tube. 
4) The eyepiece of a microscope is a concave lens. 
Select the correct answer using the code given below.