An Industry Has 1000 Competitive Firms, Each Producing 50 Tons

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