The answer should be B. A half step
A comet is the loose, icy body with a long, narrow orbit.
Comets are very small solar system body made mainly of ices mixed with smaller amounts of dust and rock. Most comets are not larger than a few kilometers across. The main body of the comet is called the nucleus, and it can contain water, methane, nitrogen and other ices. Their speeds vary depending on their orbits and where they are in it. The closer they are to the sun, the faster they are going.
Is a process in which One set of substances, called REACTANTS, is converted to a new set of substances is called PRODUCTS.
--In other words, a chemical reaction is the process by which a chemical change occurs.
Gregor Mendel was the first person to trace the characteristics of successive generations of a living thing.