An industry has 1000 competitive firms, each producing 50 tons of output. At the current market price of $10, half of the firms have a short-run supply curve with a slope of 1; the other half each have a short-run supply curve with slope 2. The short-run elasticity of market supply is
A) 1/50 B) 3/10 C) 1/5 D) 2/5 E) none of the above