Design a device that will knock a block of wood a distance of 5 meters.

That was the challenge in science class. Ben and Sam designed a pendulum to move the wood block. Their first design moved the block about 1.5 meters. They rebuilt their pendulum and changed the mass of the pendulum bob. After they made several changes in the mass of the bob, they finally knocked the wooden block 7.0 meters.
Each time Ben and Sam tried a new mass for the pendulum bob they were
A) designing a product.
B) identifying a problem.
C) evaluating the design.
D) implementing the design.