A Piece of Taffy Slams into and Sticks to Another

Multiple Choice

A piece of taffy slams into and sticks to another identical piece of taffy that is at rest. The momentum of the two pieces of taffy stuck together after the collision is the same as it was before the collision. Kinetic energy is a different story, for part of it turns into heat. What percentage of the kinetic energy converts into heat?

A) 0%
B) 25%
C) 50%
D) 75%
E) not enough information