When a stretched string is released, the potential energy in the string is converted to

 Kinetic energy

Explanation:

Potential energy is converting into a kinetic energy while stretching. Those energies can be converted one into another, kinetic to potential and potential to kinetic. Potential energy is found in the objects and the kinetic one is the energy that is found in that object that is moving.

We have also gravitational potential energy and this energy is found when an object falls from somewhere, then, this energy is changed into kinetic energy.

Answerencaustic and fresco;

That is true  i hope that : )