Your best choice seems to be D)
Answer:All elements with 84 or more protons are unstable; they eventually undergo decay. Other isotopes with fewer protons in their nucleus are also radioactive.
Explanation:
I believe it's C. Amino acid is a monomer not a polymer. Q2 is B. Q3 I believe is A. Q4 is D.
The correct answer is A.
Hunger, chemical imbalance, and blood levels are all internal issues. Cat dander on the other hand is not something the body creates or and is something in the environment.
Thus, your answer is A.