Rizhao Medical Equipment Spring

A, the metal spring in the flashlight plays the role of a wire. If it is changed to a plastic spring, plastic is a non-conductive insulator, which will cause an open circuit and the light bulb cannot emit light, so A is incorrect;

BC, metal spring is a wire, which can't convert elastic potential energy into electric energy and electric energy into light energy, so BC is incorrect;

D, metal spring has elasticity and conductor at the same time, which can prevent the circuit from breaking due to poor contact, so D is correct.

So choose d