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 stuck together after the collision is the same as it was before the collision, but this is not true of the kinetic energy, which is partly turned into heat. What percentage of the kinetic energy is turned into heat?

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