On a Smooth Horizontal Floor,an Object Slides into a Spring

Multiple Choice

On a smooth horizontal floor,an object slides into a spring which is attached to another mass that is initially stationary.When the spring is most compressed,both objects are moving at the same speed.Ignoring friction,what is conserved during this interaction?

A) momentum and mechanical energy
B) momentum only
C) kinetic energy only
D) momentum and kinetic energy
E) momentum and potential energy