The diagram is being used to illustrate the second law of thermodynamics, where qh represents a hot object and qc represents a cold object.

a black box on the left labeled q subscript h baseline and a touching white box on the right labeled q subscript c baseline.

which will best complete the diagram to illustrate the law?

adding in the boxes an arrow that points from qh to qc
adding in the boxes an arrow that points from qc to qh
adding in the boxes an arrow that points in both directions between qh and qc
adding in each box an arrow that points upward from qh and from qc

the correct answer is a. adding in the boxes an arrow that points from qh to qc