39. Quantity demanded, expressed as a function of the market price is given by Q = a + bP. The price elasticity of demand , at the equilibrium price P and quantity Q , is (A) (1/a)(P /Q ). (B) (1/b)(P /Q ). (C) (b/a)(P /Q ). (D) (a/b)(P /Q ). (E) b(P /Q ).