It would be D, fertilization.
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! =)
Wear safety goggles while looking into the opening of the test tube
Six <span>characteristics are used to describe living things.
</span>To be considered alive, an object must exhibit all of the characteristics<span> of
</span>living things<span>.</span>
B. 6
