1,000 identical drops of oil of density 500kgm^-3 have a total mass of 5 x 10^-4kg. One of the drops forms a thin film of area 0.5m² on water. The thickness of the film is

• A.2 x 10^-8m
• B.2 x 10^-9m
• C.2 x 10^-7m
• D.3 x 10^-9m
• E.2.8 x 10^-8m