A $2\mathrm{.}0-kg$ block is attached to one end of a spring with a spring constant of $100\frac{N}{m}$ and a $4\mathrm{.}0-kg$ block is attached to the other end. The blocks are placed on a horizontal frictionless surface and set into motion. At one instant the $20-kg$ block is observed to be traveling to the right with a speed of $0\mathrm{.}50\frac{m}{s}$ and the $4\mathrm{.}0-kg$ block is observed to be traveling to the left with a speed of $0\mathrm{.}30\frac{m}{s}.$ Since the only forces on the blocks are the force of gravity, the normal force of the surface, and the force of the spring, we conclude that:

the motion was started with the masses at rest

the motion was started with at least one of masses moving

the motion was started by compressing the spring

the spring is not compressed at the time of observation

the spring is compressed at the time of the observation