What does it mean to say that a plant community provides ecosystem services?
a. it increases npp.
b. it improves the ability of the abiotic environment to support life.
c. it increases species richness.
d. it provides economic gain for humans.

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.

the sugar-phosphate backbone forms the structural framework of nucleic acids, including dna and rna. this backbone is composed of alternating sugar and phosphate groups, and defines directionality of the molecule.