A closed system is a system that makes no physical or chemical exchanges with its environment. Of these systems provided as choices (tree, human, clock, car), only a clock does not make exchanges with the environment, except for energy.
Therefore, of that list, only a clock would be a closed system.
Hope that helped! =)
Answer:
Their skeletal structure and possibly how they look but usually not. You can also look at the way they live and the biomes they live in.
Explanation:
Much like a cell, a virus is able to grow and reproduce in large numbers
A virus is a microscopic nonliving parasite that only reproduces inside the cells of living hosts. Like cells, viruses have the ability to grow and reproduce within the host cell. When a virus infects a host cell, it injects its genetic material into the cell and forces the host cell to produce thousands of similar copies of the original virus.