Final answer:
The two true statements about a system are that it is a group of objects analyzed as one unit, and that energy transferring across system boundaries is conserved.
Step-by-step explanation:
Out of the given statements about a system, the ones that are true are: a. A system is a group of objects analyzed as one unit, and b. The energy that moves across system boundaries is conserved. A system can indeed be thought of as a single object or a collection of objects that are considered as having no internal structure (Essential Knowledge 5.A.1), and it is crucial to understand that the energy of a system is conserved when it is transferred across its boundaries (Enduring Understanding 5.B). This conservation of energy aligns with the first law of thermodynamics, a fundamental concept in Physics.
Although systems can be naturally occurring or man-made, statement d. All systems are made by humans, is incorrect because natural systems such as a solar system or a biological ecosystem exist without human intervention. Statement c. There's only one way to define the boundaries of a system, which is also not true as the boundaries of a system can be defined in various ways depending on what is being studied.