A greenhouse is used to protect plants by keeping them warm.
Hobby greenhouses used to be small glass houses or fiberglass buildings.
Glass or fiberglass buildings are used to protect plants by keeping them warm.
Glass or fiberglass buildings are used to protect plants by keeping them what?
(1) mild
(2) heat
(3) hibernating
(4) cooled
(5) warm
(6) warmth
(7) cold
(8) frozen