A $5-kg$ object is moving to the right at $4\frac{m}{s}$ and collides with another object moving to the left at $5\frac{m}{s}.$ The objects collide and stick together. After the collision, which of the following is guaranteed to be true of the combined object:

Select one:

a$.$ is moving to the right

b$.$ is moving to the left

c$.$ has less kinetic energy than the system had before the collision

d$.$ is at rest