Which of the following best expresses the definition of a closed system? energy can enter or leave the system but matter cannot. heat and matter are both able to enter or leave the system. matter can enter or leave the system but energy cannot. heat and matter can enter the system but cannot leave the system.

The correct option is this: ENERGY CAN ENTER OR LEAVE THE SYSTEM BUT MATTER CAN NOT.
A closed system is one in which mass is conserved within the boundaries of the system, but energy can enter or leave the system. Thus, in a closed system, the mass of the matter remains constant, matter is not allow to come in, matter is not allow to escape from the system.

Organisms are more likely to be more preserved in mud than sand because mud is moist and wet, while sand is very dry.