Possible answers:
[a]. cellulose.
[b]. Species.
[c]. orchids.
[d]. the sun.
[e]. h2o.
[f]. organisms.
[g]. glass.
[h]. our planet.

Fact 1: Agreenhouse is used to protect plants by keeping them warm. Fact 2: Many orchids are rewarding indoor plants. Given the two facts above, what is a greenhouse used to protect?
Answer:
[c].