In a system with two blocks connected by a string over a pulley, how does the tension in the string connecting the two blocks vary when the blocks are in motion?
A) The tension is equal to the weight of the heavier block.
B) The tension is constant and equal to the weight of both blocks combined.
C) The tension is equal to the weight of the lighter block.
D) The tension varies depending on the acceleration of the blocks and the mass of each block.