The expression "A + B <--> C + D" represents a chemical equation. A chemical equation represents the "mixture" of molecules or elements that will react and form other molecules and elements, so we can say that A, B, C and D represent molecules or elements.
But not only that. In a chemical equation, the elements and molecules that are before the symbol "<-->" represent the reagents in the equation. Therefore, A and B are the reagents. The elements or molecules found after the symbol "<-->" are the products of the reaction. Therefore, C and D are the products.
(In most cases) A child from red+black haired parents would have black hair. The allele for black hair is dominant to that of red, and would be the phenotype of the hair.
Sphenoid bone spans the width of the cranial floor; keystone of the cranium because its central wedge articulates with every other cranial bone. Unlimited access.
