Final answer:
The best example of a closed system is the astronaut's spacesuit, which provides a self-contained environment for an astronaut in space.
Step-by-step explanation:
The best example of a closed system among the given options is the astronaut's spacesuit.
A closed system is one that does not exchange matter or energy with its surroundings. The astronaut's spacesuit is designed to provide a self-contained environment for an astronaut in space. It is sealed off from the vacuum of space and provides oxygen, temperature regulation, and pressure control for the astronaut.
On the other hand, a water treatment plant and a desert are not closed systems. A water treatment plant receives water from various sources and treats it for consumption, releasing treated water and waste products. A desert is an open system where matter and energy flow in and out through various processes.
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