A student focused the image of a distant object using a device ‘X’ on a white screen ‘S’ as shown in the figure. If the distance of the screen from the device is 40 cm, select the correct statement about the device. 

• The device X is a convex lens of focal length 20 cm.

• The device X is a concave mirror of focal length 40 cm.

• The device X is a convex mirror of radius of curvature 40 cm.

• The device X is a convex lens of focal length 40 cm.