ANSWER
3) elastic energy
Step-by-step explanation
When the gymnast reaches the trampolin, both the gymnast and the trampolin move down because of the elasticity of the trampolin, until the trampolin is at its maximum point of which it can stretch. At this point the gravitational energy of the gymnast is zero because of zero height and its kinetic energy is zero too, because of zero energy. Therefore all the energy is stored as elastic energy.