Which two statements are true about a system?

a system is a group of objects analyzed as one unit.

energy that moves across system boundaries is conserved.

there’s only one way to define the boundaries of a system.

all systems are made by humans.

The first choice i correct. The second is also correct as it should obey the Law of Conservation of mass. The third choice is incorrect. It depends on the nature of the system. For example, for an ideal gas, you can define at least 2 parameters to set the system boundaries. The fourth choice is incorrect, a system can be theoretical or practical. Hence, the answers are the first and second choices.

A., d., and f i think