Correct answer is option D.

A sheet of glass is  made by floating molten glass on a bed of molten metal, typically tin, although lead and other various low-melting point alloys are also used. This method gives the sheet uniform thickness and very flat surfaces.

Modern windows  are made from float glass. Most float glass is soda-lime glass, although relatively minor quantities of specialty borosilicate and flat panel display glass are also produced using the float glass process.