Answer:
Environment.
Explanation:
A greenhouse essentially allows the farmer/user to control the temperature, humidity, and others such as soil. The environment is key when growing food that:
1) Does not grow in the climate
2) Is not native to the place, and would need different treatment per what is used natively.
Without a greenhouse, it may also be harder to grow food during off season, which would lead to a decrease amount of food generated compared to with one. However, that is not to say Greenhouse's do not have their drawbacks. it is extremely expensive to use especially with the energy they use to generate the needed temperature to keep the crops alive.
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