a) Flat Film Extrusion
b) Blown Film Extrusion
c) Slit Die Extrusion
d) Cast Film Extrusion

Answer: b
Explanation: Tubular Extrusion is also known as Blown Film Extrusion. Flat Film extrusion is also known as Cast Film and Slit Die Extrusion. Like Flat Film Extrusion, Tubular extrusion is also used to convert extruded plastic into sheets. It is done by blowing air through the center of tubular die, due to which the thin tube from extruder is inflated into a thin bubble and cooled, after which it is flattened and wound up.