B I think because it would have to be 25% so then Aa would be appropriate as of it's recessive.
D. Number of protons in an atom's nucleus
<span>Definition of Compound. ... The type of bonds holding elements together in a compound can vary: two common types are covalent bonds and ionic bonds. The elements in any compound are always present in fixed ratios. Example 1: Pure water is a compound made from two elements - hydrogen and oxygen.</span>