question... If a tumor has formed, this gene might have mutated:
Options:
- (A) p53
- (B) SNPs
- (C) OCA 2
- (D) DNA
- (E) gene
- (F) tRNA
- (G) malignancy
- (H) TRH
answer... Cells that divide uncontrollably may form a tumor, or abnormal mass of cells. When p53 is mutated, cells divide uncontrollably. When p53 is mutated a tumor may form.
The answer is (A)

question... What grows into the soil to absorb water and minerals? 
Options:
- (A) NaCl
- (B) vegetation
- (C) burrs
- (D) Trees
- (E) grass
- (F) Carrots
- (G) Conifers
- (H) potatoes
answer... Most plants grow roots down into the soil to absorb water and minerals. Beets and carrots are the roots of plants. Most carrots grow down into the soil to absorb water and minerals.
The answer is (F)

question... What are a source of food for many fish species?
Options:
- (A) layers of fat
- (B) bird species
- (C) human species
- (D) keystone species
- (E) Organic compounds
- (F) barnacles
- (G) gastropod shells
- (H) species of deer
answer...

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Sponges are a source of food for many species of fish. Sponges are also keystone species. Keystone species are a source of food for many fish species.
The answer is (D)