Cell membrane fluidity is determined by many things, including the presence of or absence of saturated and or unsaturated fatty acid tails, and because of that the ability of the phospholipids in a cell membrane to tightly pack together or not. I believe though in terms of an additional substance it would have to be cholesterol. These specific lipid molecules are inserted in between the phospholipids preventing phospholipids from tightly packing together thus allowing the cell membrane to have greater fluidity and flexibility.
Radioactivity is the emission of a particle from am atom. Fission is splitting an atomic fusion is combining two nuclei into a new atom and a meltdown refers to a disaster at a unclear power plant. Your answer is D.
That'll be guanine. If you look up "pyrimidine" in google, it will tell you the two nucleotides that are pyrmidines are cytosine and thymine. So that leaves guanine.
If you have a set of choices my best answer would be traits.
